scientific research on essential oils

March 7, 2020

Do Essential Oils Work? Here’s What Science Says

Every time you turn around someone is suggesting aromatherapy. Essential oils are a $1 billion industry, but are they effective?

By Everyday Einstein Sabrina Stierwalt

Madeleine Steinbach Getty Images

Your friend suggests that you use a lotion infused with peppermint essential oil to help combat your nausea. Your coworker insists that he has never slept so well since starting to sprinkle a little lavender oil on his pillow at night. Last year alone consumers in the United States  spent $1 billion on essential oil products  and is expected to  exceed $11 billion  by the year 2022. But what does the research say? Do essential oils really work?

What is aromatherapy?

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Essential oils are oils, typically fragrant ones, that have been extracted from the roots, flowers, leaves, or seeds of plants using steam or applied pressure. The qualifier “essential” refers to the fact that the oil contains the “essence” of the plant (i.e. the natural chemicals that provide a distinct odor or flavor). In the practice of aromatherapy, these oils—once diluted—are applied to the skin, smelled, dabbed on a pillow or in a bath, or heated so that their aroma is dispersed into the air. Some soaps and lotions can also be made with essential oils and used as aromatherapy products.

The use of essential oils is cross-cultural and dates back thousands of years. Many know the story of frankincense being offered as one of the gifts of the Magi. Even if you haven’t purchased an essential oil roller or diffuser, chances are you may have used them anyway.  Vick’s Vaporub , typically rubbed on the chest as a cough suppressant, contains the essential eucalyptus, cedarleaf, and nutmeg oils (among others) suspended in petroleum jelly.

Do essential oils and aromatherapy work?

The National Institute of Health provides a thorough summary via the US National Library of Medicine of  research conducted into the efficacy of essential oils . Currently, there is no evidence-backed research showing any illnesses that can be cured through the use of essential oils or the practice of aromatherapy. The results on the other possible benefits of essential oils as, for example, mood elevators or stress relievers, are more mixed. But most are still inconclusive.

One of the scientific studies that have revealed positive results from essential oils involves patients with dementia. Although, contrary to common lore, drinking a tablespoon of  fish oil every day won’t likely stave off dementia , there is evidence that balm from  lemon oil reduces agitation  in patients with dementia according to a study in the Journal of Clinical Psychiatry.

There are other proven success stories for essential oils, such as the  treatment of acne with tea tree oil  and the  treatment of alopecia areata or hair loss with oils  like thyme, rosemary, lavender and cedarwood.

Research into the use of essential oils found in citrus fruits is particularly intriguing due to their natural antibacterial qualities. For example, citrus oil, particularly when combined with Dead Sea salts, was shown to  inhibit bacterial growth  in mice and act as an anti-inflammatory agent. The citrus essential oil  bergamot could help fight the growth of common causes of food poisoning  like listeria, e coli, and staphylococcus.

However, most of these studies have not yet extended to clinical trials, meaning there is still much more work to do before essential oils would be potentially prescribed by physicians. Given the strong public interest in essential oils, whether it be to target things other medicines have so far failed to fix (like migraines, anxiety, stress, insomnia, and memory) or to control what goes into their medicine cabinet without a prescription, more research into the possible benefits of essential oils is clearly worthwhile.

There are very few noted side effects associated with the use of essential oils, although in the US they do not require approval from the  FDA . One exception is the estrogen-like effects noted for lavender and tea tree oils which have been linked to  breast enlargement  in pre-pubescent boys when applied over long periods of time.

So if you’re looking to relieve stress, adding a few drops of diluted essential oils to a warm bath probably doesn’t hurt. But before you spend $40 on a 15-mL bottle, you might want to try a scented candle first.

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Review article, essential oils: a systematic review on revolutionizing health, nutrition, and omics for optimal well-being.

• 1 NovaVita, Guayaquil, Ecuador
• 2 Laboratorio para Investigaciones Biomédicas, Facultad de Ciencias de la Vida, Escuela Superior Politécnica del Litoral (ESPOL), Guayaquil, Ecuador

Purpose: Essential oils from various plants have diverse therapeutic properties and are researched extensively. They have applications in medicine, aromatherapy, microbiology, agriculture, livestock, and the food industry, benefiting the population.

Methods: This systematic review followed the PRISMA verification protocol. The study focused on the anti-inflammatory effects, nutraceutical properties, antioxidant and antibacterial activity of essential oils in lemon, orange, cumin, cinnamon, coriander, rosemary, thyme, and parsley. We also looked at their presence in the diet, their effect, their mechanism of action on health, and the most important active compounds. The search was conducted in the PubMed database for the last 12 years of publications, including in vitro , in vivo , and online cell model tests.

Results: Essential oils have been shown to have multiple health benefits, primarily due to their antimicrobial and anti-inflammatory effects. The mechanism of action of cinnamon oil alters bacterial membranes, modifies lipid profiles, and inhibits cell division, giving a potential benefit in protection against colitis. On the other hand, a significant improvement was observed in the diastolic pressure of patients with metabolic syndrome when supplementing them with cumin essential oil. The antimicrobial properties of coriander essential oil, especially its application in seafood like tilapia, demonstrate efficacy in improving health and resistance to bacterial infections. Cumin essential oil treats inflammation. Parsley essential oil is an antioxidant. Orange peel oil is antibacterial, antifungal, antiparasitic, and pro-oxidative. Lemon essential oil affects mouse intestinal microbiota. Thyme essential oil protects the colon against damage and DNA methylation. Carnosic acid in rosemary oil can reduce prostate cancer cell viability by modifying the endoplasmic reticulum function.

Conclusion and discussion: Essential oils have many therapeutic and antiparasitic properties. They are beneficial to human health in many ways. However, to understand their potential benefits, more research is needed regarding essential oils such as coriander, parsley, rosemary, cumin, and thyme. These research gaps are relevant since they restrict understanding of the possible benefits of these crucial oils for health-related contexts.

1 Introduction

Essential oils (EOs) are fragrant extracts obtained from various plants. Their composition varies depending on the plant species from which they are extracted. It is estimated that more than 200 compounds may be present in these oils. In recent years, essential oils have gained significant popularity in various industries, such as aromatherapy, food flavoring, and natural pharmacological treatments, due to their numerous uses, primary components, and respective properties. Consequently, several applications have been studied, including their antimicrobial, anti-inflammatory, analgesic, and antioxidant properties ( 1 ).

The main bioactive compounds of EOs are terpenes and terpenoids, which are responsible for the biological activities mentioned above ( 2 ). So, the properties of EOs contribute to the prevention of diseases through different mechanisms of action. In vitro studies are generally carried out, and it has been shown that the anti-inflammatory components of EOs inhibit free radicals that can generate mutations alone. In the DNA. Likewise, when there is prolonged oxidative stress, an excessive accumulation of reactive oxygen species (ROS) can trigger chronic disorders such as metabolic syndrome, cardiovascular diseases, diabetes, and even cancer for the same reason that there are mutations in the DNA. EOs rich in polyphenols and their antioxidant properties act as therapeutic agents for these diseases ( 3 ).

Essential oils are used in healthcare to treat specific diseases or health conditions. They can be used to alleviate symptoms associated with conditions such as Alzheimer’s, cardiovascular diseases, sleep/stress disorders, and pain during childbirth ( 4 ). Research has shown that rosemary essential oil has potential anticholinesterase inhibitory and antioxidant effects that may help protect the brain from chronic anticholinesterase diseases such as Alzheimer’s. However, more studies are needed to determine the adverse effects or benefits. Additionally, aromatherapy has been found to improve cognitive function in patients with such conditions ( 5 ).

Antimicrobials are used for various purposes, including medical use as antiviral agents, immunomodulators, and antibiotics. They are also used as food preservatives due to their antimicrobial and antioxidant properties, which help counteract skin infections and, in addition to preventing food spoilage, are used to combat microorganisms that could be transmitted through food ( 4 ). According to Swamy et al. ( 6 ), lemon has antiviral properties against the influenza virus, while cinnamon is effective against enterobacteria.

Essential oils can affect bacteria differently, depending on their chemical components. Some oils can kill the bacteria (bactericidal action), while others can only slow their growth (bacteriostatic action). Essential oils can also affect cellular processes, such as nutrient processing, molecule synthesis, and regulation of biological processes between cells. Many plants with these characteristics are still being studied, and more findings are expected as they are widely used. These plants include cinnamon, thyme, rosemary, lemon, orange, cumin, and parsley ( 4 ). This systematic review identifies literature from the past 10 years to highlight their uses and effects on health, diet, microbiota, and mechanism of action.

This systematic review follows the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analysis) verification protocol ( 7 ) with keywords in the search strategy as Essential oils, Nutrition, Omics, Bioactive Compounds, Well-being, properties, Application in Foods previously published experimental and/or clinical case trials in mouse models and/or cell lines and studies in human participants were used along with the use of search operators AND, OR. The study focuses on the anti-inflammatory effects, nutraceutical properties, antioxidant, and antibacterial activity, presence in food, effect and mechanism of action on health, and the most important active compounds of essential oils such as lemon, orange, cumin, cinnamon, coriander, rosemary, thyme, and parsley by searching for articles conducted in a cell line ( in vitro ), mouse model, in vivo specifically in PubMed database.

The study selection process was conducted in two stages. In the first stage, three authors independently reviewed the titles and abstracts of the studies based on the inclusion and exclusion criteria. They identified the studies that met the inclusion criteria and excluded the ones that did not. In the second stage, two authors thoroughly screened all the full articles and excluded the studies that did not meet the inclusion criteria. We developed custom search strategies for the PubMed bibliographic database. The search was conducted directly and included all articles published within the last 12 years without language restrictions. Additionally, we thoroughly examined the reference lists of the selected articles to identify any relevant research that may have been missed during the electronic database search. Three authors gathered the required data from the reports that had been selected. For all incorporated studies, the following details were recorded: author(s), year of publication, type of essential oil, its impact on health, its effects on health, and its presence in the diet. The authors independently reviewed all full articles.

3 Eligibility criteria

3.1 inclusion and exclusion criteria.

Studies were considered eligible if they met the following criteria: (1) retrospective experimental and clinical studies in human subjects and mouse models and/or cell lines, (2) studies investigating the health benefits of the essential oils described above, (3) studies with quantitative and qualitative data, (4) studies without any language restrictions, (5) systematic reviews, and (6) manuscripts in journals with an impact index.

The following studies were excluded: (1) not meeting the objectives of the article, (2) university theses, (3) not meeting the search criteria, (4) book chapters or books, (5) review articles published more than 12 years ago, and (6) studies not found in the database described above.

3.2 Search strategies

To refine the search, specific keywords such as “Essential oils” “Nutrition” “Omics” “Bioactive compounds” “Food application “Wellness” “properties” “mouse models ““experimental” “clinical” “cell lines” were used together with the use of search operators (Nutrition* OR “dietary” OR “nutritional* content” OR “macronutrients” OR “macronutrients” OR “diet”) AND (“Essential oils*” OR “volatile oils* “OR “Extracted oils* OR “Aromatherapy oils*” OR “Plant oils* “) AND (“Essential oils*” OR “Plant oils*” OR “macronutrients” OR “diet”) AND (“Essential oils*” OR “volatile oils* “OR “Extracted oils* Aromatherapy oils*” OR “Plant oils*) AND (Omics* OR “Microbiota*” OR “Genomics*” OR” Metabolomics*”) AND (Bioactive compounds* OR “Functional ingredient” OR “Major active compound *” OR “Active substance” OR “Health-promoting compound*”) AND (Food application * OR “Application in Food Safety “OR “Application in Food Industry”) AND (Wellness* OR “health “) AND (properties* OR “Aspects “OR “Traits”) performed in electronic databases such as Pubmed, ScienceDirect and Scopus.

4.1 Study selection

In the first phase of study selection, 107 citations were found in the PubMed electronic database. After thoroughly reviewing the abstracts, we excluded 27 articles with 12 duplicates. We then identified 85 additional articles through PubMed and reviewed their full text. Thus, this study included 80 references ( Figure 1 ).

Figure 1 . Flow diagram of literature search and selection criteria for essentials oils from PRISMA.

4.2 Study characteristics

The table below summarizes the key features of the studies analyzed in this research. These studies were conducted in different countries and published between 2011 and 2023 in both English and Spanish. It was observed that the number of publications increased significantly from 2019. All the selected studies were focused on essential oils, with most of them investigating the properties of these oils, such as their antimicrobial and anti-inflammatory effects. The studies have produced significant findings on the benefits of using essential oils, including inhibiting pathogenic microorganisms, preventing radical formation, acting as natural antioxidants and antimicrobial agents, exhibiting anticancer effects in the intestinal microbiota, and preserving food naturally.

Table 1 shows the type of food used, the analysis of the major active constituent identified, and relevant results in the essential oils performed in vivo or in vitro . The main groups of constituents were in cinnamon essential oil cinnamaldehyde, coriander essential oil β-linalool, camphor, geranyl acetate, and cymene; in cumin essential oil cumin aldehyde, and parsley essential oil myristicin, apiole, α-pinene, and β-pinene. Table 2 shows the most predominant bioactive compounds, their health effects, and tentative mechanisms. The main compounds in lemon and orange essential oils are limonene. In cinnamon essential oil, cinnamaldehyde; in Cilantro essential oil, linalool; in Parsley essential oil, myristicin; in Rosemary essential oil monoterpenes; in Thyme essential oil, thymol with antioxidant activity, antimicrobial, inflammatory activity, and innate immune responses.

Table 1 . Essential oils and their used as food.

Table 2 . Actions in the health of the essential oils.

Table 2 shows how this essential oil affects health, the analysis of the major active constituent identified, and relevant results in the essential oils performed. The lemon essential oil has been found to contain a significant amount of limonene, which has strong antioxidant properties and can help eliminate DPPH radicals ( 16 ). Research has shown that it can also be effective as a food preservative, with concentrations of 0.06 and 0.312 mg/g potentially preventing the growth of pathogenic bacteria like L. monocytogenes ( 15 ). Limonene may also positively affect the immune system and intestinal microbiota ( 25 ). On the other hand, orange essential oil is also a natural citrus preservative in food due to its antimicrobial properties. Its main compounds, citral, and linalool, have been found to have superior effects on intestinal microbiota in mice when compared to lemon essential oil ( 17 ). It is important to note that further research is needed to fully understand the potential benefits of these essential oils in the areas mentioned. And findings regarding essential oils like parsley, cumin, coriander, thyme, and rosemary were relatively scarce, mostly showing effects on health. Mainly, parsley exhibits both antioxidant and prooxidative behavior, making it a promising subject for further investigation. Cumin, with volatile compounds inhibiting neutrophil activation, is strongly associated with treating inflammatory pathologies. Supplementation with cumin in patients with metabolic syndrome is estimated to decrease diastolic pressure ( 12 ). Coriander is known for its resistance to bacterial infections and tends to improve health in tilapia ( 10 ). Thyme demonstrated inhibition of cell proliferation, varying with the dose in all evaluated tumor cell lines ( 26 ).

Table 3 highlights the various omics mechanisms of the essential oils already mentioned above. The essential oils of lemon, orange, and cinnamon influence the intestinal microbiota in the same way the essential compounds of coriander inhibit the activity of gastrointestinal pathogenic bacteria. The essential compound of rosemary oil has an anti-Warburg effect on gastric carcinoma, dose, and time. And a thymol compound-dependent cytotoxic effect on cancer cell lines PC-3, DU145, MDA-MB-231, and KLN205.

Table 3 . Essential oils and omics mechanism.

5.1 Health benefits

In a study by Mohammed et al. ( 19 ), six groups of male rats were treated orally for 4 weeks. The control and STZ-treated groups were compared with groups that received low or high doses of cinnamon oil emulsion (COE; 200 or 400 mg/kg Bw) and groups of STZ-treated rats that received COE in low or high doses. The results showed a significant decrease in fasting blood glucose levels, plasma C-peptide, serum triglycerides, total cholesterol, and blood urea nitrogen, with a substantial increase in high-density lipoproteins after 35 days. Glucose tolerance improved, and an increase in pancreatic islet β cells was observed. Both doses improved glucose, insulin, SOD, GSH, amylase, lipid profile, and hepatic MDA levels. Positive histological changes were also observed in the liver and pancreas. The current results revealed that cinnamon oil emulsion (COE) produced more than 1% of total volatile compounds, and GC/MS identified 16 compounds. More than 86% of these volatiles originated from 5 volatiles and included cinnamaldehyde (88.7%), 1,8 cineole (2.02%), acetic acid, 1,7,7trimethylbicyclo [2.2.1] heptyl ester (1.79%), α-Pinene (1.45%), and α-Terpineol (0.92%). This research aimed to examine the potential of essential oils as antitumor agents. In vitro models, including phosphomolybdenum, DPPH, and H2O2 methods, were used to achieve this. This study used BHT (butylhydroxytoluene) and ascorbic acid (vitamin C) as positive controls for comparison ( 20 ).

5.2 Food benefits

This review focuses on analyzing the effects of cinnamon oil when used as an additive in poultry feed, addressing its influence on various aspects such as bird performance, carcass characteristics, meat quality, its impact on cholesterol reduction, its antioxidant activity, its effects on immunity and considerations related to microbiology. The key results of this research indicate that including cinnamon essential oil extracts as additives in poultry feed carries notable benefits in terms of improved performance, reduced blood cholesterol levels, and increased activity: antioxidant, immunity booster, and favorable microbiological considerations. Cinnamon could represent a viable alternative to antibiotics, providing excellent safety in aspects related to animal health, the environment, and the economy in the poultry industry. Furthermore, it was observed that the main component of cinnamon oil is Cinnamaldehyde, which approximately represents Cinnamaldehyde (88.2%), eugenol (1.0%), and benzyl alcohol (8.0%) in its composition ( 34 ).

5.3 Actions in health

One of the potential health benefits is protection against colitis, which is an anti-inflammatory bowel disease. This is related to the mechanism of action, antimicrobial activity, and anti-inflammatory effect of cinnamon due to the alteration in the bacterial membrane, modifications in the lipid profile, and the inhibition of cell division, as shown in a mouse model study. Cinnamomum osmophloem reduced the expression of Toll-like receptor 4, myeloid adapter protein 88, and nuclear kinase in mice with colitis that had received endotoxin, suggesting an anti-inflammatory effect. In addition, it was identified that the predominant active component in cinnamon essential oil is cinnamaldehyde, which constitutes approximately 68.95% of its composition ( 31 ).

6.1 Health benefits

In a study conducted by Helal et al. ( 21 ) on the motility of third-instar larvae (L3) belonging to the Trichostrongylidaeindicate that these essential oils and their components, such as linalool (68.03%), α-tinene (9.71%), γ-terpinene (10.48%) and camphor (11.76%), could effectively combat infections caused by helminths.

Moreover, studies have shown that essential oils, including cilantro oil, can effectively hinder the growth of clinical strains of dermatophytes belonging to two primary genera, Microsporum and Trichophyton , for up to 21 days. It is worth noting that accurately identifying the specific individual is crucial ( 22 ).

6.2 Food benefits

The antioxidant, antimicrobial, and anti-biofilm properties of the essential oil obtained from cilantro ( Coriandrum sativum L. ) are the most studied concerning its possible application in food. The main volatile components identified in coriander essential oil in an in vitro study were mainly β-linalool, which accounted for 66.07% of the total content, showing a high antioxidant activity with an inhibition percentage of 51.05% in eliminating radicals. Its antibacterial activity presented the most effective against B. subtilis, followed by S. maltophilia and Penicillium expansum ( 9 ). An in vivo study assessed the effectiveness of adding 1% coriander oil to tilapia feed to enhance health and immunity against bacterial infections. The key compounds in this oil were linalool and geranyl acetate ( 10 ).

7.1 Health benefits

Recent studies have shown that cumin oil can potentially suppress neutrophil activation, which could be beneficial in treating inflammatory diseases that involve high levels of neutrophil activity. This includes respiratory burst and degranulation induced by formylpeptide receptor agonists fMLF/CB and MMK1 in human neutrophils. These effects’ mean inhibitory concentration (IC50) ranges from 3.8 to 17.2 μg/mL. Additionally, it has been noted that cumin oil contains a high percentage of cumin aldehyde, which makes up 49.9% of its composition ( 11 ). Morovati et al. ( 12 ) found that cumin essential oil significantly reduced diastolic blood pressure in patients with metabolic syndrome after 8 weeks of treatment.

8.1 Health benefits

Parsley essential oil exhibits an antioxidant profile due to its higher percentage of DPPH radical inhibition and FRAP value; however, it also showed pro-oxidative behavior according to the TBARS test. On the other hand, parsley essential oil demonstrates more significant bacterial activity after lavender. The main components were myristicin (36.15%), apiole (20.97%), α-pinene (15.47%), and β-pinene (10.43%). The presence of alkyltetramethoxybenzene, limonene and elemicin (6.45, 4.74 and 2.74%, respectively) was also relevant ( 13 ).

9.1 Health benefits

It has been shown that the essential oil obtained by hydrodistillation of discarded lemon leaves contains enough chemicals can inhibit the growth of harmful microorganisms such as C. albicans, L. monocytogenes , and S. aureus . The oil’s most abundant components are limonene (with a concentration of 260.7 mg/mL), followed by geranial (102.6 mg/mL) and neral (88.3 mg/mL). The study also found that a concentration of 25 μM of the oil led to a significant reduction in cell viability, with a 33% decrease in HeLa cells and a 27% decrease in A375 cells. This was also accompanied by notable changes in cellular morphology ( 14 ).

The main components of lemon essential oil responsible for its antibacterial and antioxidant properties are terpenoids, with d-limonene being the most abundant. D-limonene exhibits the highest antioxidant capacity and effectively removes DPPH radicals ( 16 ).

9.2 Food benefits

In the food industry, lemon essential oil’s antioxidant and antimicrobial properties can be used as a preservative. According to Ben Hsouna et al. ( 15 ), the application of this oil at concentrations of 0.06 and 0.312 mg/g presents promising potential for the prevention of contamination and the development of pathogenic bacteria, especially L. monocytogenes , which opens new perspectives in this field.

9.3 Action in health

The effect of limonin on the intestinal microbiota has been investigated in mice, and a significant increase in the diversity of the microbiota present in the colon of mice fed limonin has been observed. Thus, it was highlighted that the composition of the intestinal microbiota community was different compared to the control group. A prediction was made that limonin would positively affect the regulation of amino acid metabolism, lipids, and immune system function. It is highlighted that it can significantly suppress diseases related to the immune system and markers of infectious diseases based on its influence on the intestine ( 25 ).

10.1 Health benefits

The Citrus sinensis peel oil has potential antibacterial, antifungal, and antiparasitic effects, according to a study conducted by Anwar et al. ( 18 ). The analysis showed that the maximum inhibition zone diameter was 14 mm against E. coli , and the minimum was 10 mm against S. agalactiae . Moreover, the oil was 60% effective in inhibiting leishmaniasis at a 50 μg/mL concentration after 48 h of incubation. The oil’s antimicrobial properties were also demonstrated, suggesting its possible use as a natural food preservative or an effective treatment against various pathogenic organisms. The oil contains β-pinene (0.55%), limonene (96–98%), α-pinene (0.29%), myrcene (1.3–1.45%), and octanol (0.37–0.53%).

10.2 Food benefits

A study assessed commercial orange essential oils’ chemical compositions, antioxidant, and anti-pathogenic properties [ Citrus sinensis (L.) Osbeck ]. The study used cold pressing (EOP) and cold pressing followed by steam distillation (EOPD). The analysis revealed that both essential oils contained a high percentage of monoterpene hydrocarbons, mainly limonene (89.8 to 90.4%) and myrcene (3.1 to 3.2%). Although both essential oils had similar reducing capacities, EOP showed a more remarkable ability to eliminate free radicals. Regarding anti-pathogenic properties, both essential oils inhibited the biomass and cellular viability of Staphylococcus aureus and Pseudomonas aeruginosa in their biofilms. Additionally, both methods effectively reduced the production of elastase, pyocyanin, and quorum-sensing autoinducers, particularly in Gram-negative bacteria. These findings indicate that EOP and EOPD demonstrate significant antioxidant and anti-pathogenic properties ( 17 ).

10.3 Action in health

A recent study examined the effects of administering orange essential oil, as well as limonene, linalool, and citral, directly into the stomachs of mice. The researchers were interested in understanding how these substances might affect the mice’s intestinal microbiota and biochemical parameters. The study found that all four substances could influence the mice’s intestinal microbiota composition, with the relative proportion of Lactobacillus increasing in response to treatment. However, the mice that received limonene had a notably different bacterial composition in their cecum and colon than the other groups. These findings suggest that limonene may have a more pronounced effect on intestinal bacteria, which can lead to significant changes in blood immunological markers and short-chain fatty acid levels in mice ( 27 ).

11.1 Health benefits

Thyme essential oil (TEO) has health benefits due to its bioactive compounds. TEO nanoemulsion improves its biological activity and antioxidant properties and protects against oxidative damage and genotoxicity caused by TiO2-NP. TEO contains 17 bioactive compounds, with thymol and carvacrol being the main components ( 24 ).

11.2 Action in health

Thymol has been found to impact prostate cancer (PC-3), breast cancer (MDA-MB-231), and lung cancer cells. The antiproliferative activity of cancer cells varies depending on the dose and time of exposure. Thymol also significantly induces apoptosis in all groups, with the intensity of the response varying depending on the dose administered ( 26 ).

Likewise, the antiproliferative activity has been evaluated ( in vitro ) using three human tumor cell lines: MCF-7 (breast adenocarcinoma), H460 (lung carcinoma), and MOLT-4 (acute lymphoblastic leukemia) using the MTT assay, demonstrating a dose-dependent inhibition of cell proliferation in all tumor cell lines evaluated, and differential sensitivity between them. The main components of the essential oil included thymol (36.7%), p-cymene (30.0%), γ-terpinene (9.0%), and carvacrol (3.6%) ( 30 ).

Understanding oils’ effects on our health is crucial, particularly in preventing cellular toxicity and genotoxicity. A recent study found that essential oil compounds can offer protective benefits against oxidative and methylating damage, as seen through comet assays on colorectal adenocarcinoma HT-29 cells. While most of these compounds were found to be cytotoxic to HT-29 cells, they only reached cytotoxic levels at doses equal to or greater than 250 ppm after exposure for 24 h. The study identified thymol as the most effective component in protecting DNA against oxidative damage, while geraniol also showed promise in protecting against DNA methylation damage. This research highlights the potential of essential oil compounds, especially thymol, in protecting the colonic epithelium against oxidative DNA damage and geraniol against DNA methylation damage ( 32 ).

12 Rosemary

12.1 health benefits.

A study by Christopoulou et al. ( 23 ) assessed the chemical composition, genotoxicity, and antimicrobial, antiviral, and antioxidant properties of certain substances. The results showed that the essential oil, at concentrations of up to 5%, and the extract, ranging from 25 to 90%, did not exhibit any genotoxic effects. The essential oil and the extract also demonstrated antiviral, antifungal, and antioxidant properties. Specifically, the extract exhibited notable antibacterial properties, while the essential oil was primarily effective against S. aureus . The essential oil mainly comprised monoterpenes, constituting 95.57%, whereas sesquiterpenes only represented 4.24%.

12.2 Action in health

A study on rosmarinic acid (RA) and the anti-Warburg effect in gastric carcinoma suggested that rosemary oil may reduce glucose uptake and lactate production in cancer cells. It was found that RA inhibits the expression of hypoxia-inducible factor 1α, which is involved in the glycolytic pathway. In cancer cells, inflammation promotes the Warburg effect. However, RA reduces the production of pro-inflammatory cytokines and inflammation-related microRNAs, which suggests that RA could suppress the Warburg effect through an inflammatory pathway related to interleukin (IL)-6 and the transcription factor STAT3 ( 28 ).

Using essential oil to improve the functioning of the endoplasmic reticulum can be a helpful health action in reducing the viability of prostate cancer cells and promoting the degradation of androgen receptors. A study evaluated the effects of rosemary extract, standardized in carnosic acid, on two types of human prostate cancer cells, 22Rv1 and LNCaP, and prostate epithelial cells collected from two patients undergoing radical prostatectomy. The study found that cancer cells significantly altered endoplasmic reticulum stress proteins, while normal prostate epithelial cells did not suffer endoplasmic reticulum stress. This two-stage response suggests that standardized rosemary extract might be a preferable treatment option for cancer cells rather than normal cells.

On the other hand, some results suggest that the identified core genes, such as copalyl diphosphate synthase, phenylalanine ammonia-lyase, cineole synthase, rosmarinic acid synthase, tyrosine aminotransferase, cinnamate 4-hydroxylase, and MYB58, could play a crucial role in the metabolism of Rosmarinus officinalis . This genetic analysis provides valuable information for genetic and metabolic engineering research to improve the biosynthesis of secondary metabolites in Rosmarinus officinalis ( 33 ).

13 Discussion

This review emphasizes the significant advancements of essential oils in various fields, such as medicine and the food industry, achieved through in vitro , in vivo , and cell line studies. These breakthroughs provide valuable insights that support the continuation of research in these areas. For instance, the study evaluates the impact of rosemary essential oil extract on reducing prostate cancer cells ( 28 ). Moreover, the effects of cinnamon oil as a food additive for poultry are examined. The study explores its influences on avian performance, meat quality, cholesterol reduction, antioxidant activity, and immunity ( 35 ).

Insufficient literature exists on essential oils concerning innovative omics action mechanisms, more relevant applications in food to ensure quality, and their benefits and impact on health. Therefore, it is recommended that future research should conduct studies using cell lines ( in vivo ). This approach promotes more natural additives, thereby reducing the intake of processed additives that may adversely affect human health in the long run. These limitations are significant as they restrict understanding of essential oils’ potential benefits to improve the quality of life and address specific health-related needs in the food industry.

The potential health benefits of rosemary oil have been extensively studied and documented. Compounds included in rosemary oil, notably oleic and linoleic acid, are known to benefit cardiovascular health ( 36 ). Evidence is limited for the effects of rosemary oil on glucose. Further research, with more rigorous experimental designs and in larger populations, is required to reach more definitive conclusions about these properties ( 35 , 37 – 39 ). One of the main factors contributing to rosemary oil’s potential usage in pharmacological and biotechnological applications is its biological qualities ( 8 , 40 ). For example, natural antioxidants such as rosemary extracts have shown high thermal resistance and superior antioxidant activity compared to synthetic antioxidants ( 41 ). This makes them beneficial for preserving the quality of oils, particularly in high-heat cooking processes like frying ( 42 , 43 ). Beyond acting as food preservatives, rosemary oil components may have direct health advantages. The oil’s anti-inflammatory effects may also promote brain health by preventing neuronal cell damage ( 44 – 46 ). Ongoing research reveals rosemary oil’s multipronged therapeutic potential—from enhancing heart health to shielding brain function to inhibiting tumor growth ( 47 – 49 ).

Several studies have been conducted that provide convincing evidence of the usefulness of cinnamon essential oil, but most are in vitro or animal research. More large-scale, high-quality human clinical trials are still needed to confirm the effects, establish the optimal dose, assess long-term safety, etc. Mechanistic studies have elucidated certain pathways, such as modulation of glucose transporters, antioxidant enzymes and inflammatory markers that underlie the observed effects. However, further work is needed to elucidate the full pharmacokinetic and pharmacodynamic profile, especially of key actives such as cinnamaldehyde ( 50 – 53 ).

Most research has focused specifically on cinnamon essential oil or cinnamaldehyde-standardized bark extracts. Comparisons of potency, bioavailability, and synergies between components require further research. Despite promising gastrointestinal effects, more extensive studies through rigorous randomized controlled trials on outcomes such as ulcerative colitis, irritable bowel syndrome, and dysbiosis are needed before clinical use can be recommended ( 54 , 55 ). Safety, drug interactions, and contraindications have yet to be fully established.

Some studies demonstrate the efficacy of coriander oil against organisms such as fungi and helminths and agree that linalool e is the chemically essential compound ( 56 ). However, other chemotypes and oil compositions should also be examined, e.g., those richer in decanal, borneol, or geranyl acetate for which these comparative studies would demonstrate bioactivity that may reveal differential effects ( 57 , 58 ). In addition, more detailed analyses, especially in food matrices exploring lipid peroxidation, protein oxidation, effects on shelf life, etc., would provide additional information along with limited safety studies ( 59 – 61 ). Toxicity, pharmacokinetic, and residue level studies in food-producing animals could allow the administration of higher standardized doses to enhance health effects ( 62 – 65 ). Finally, few in vivo studies explore the bioavailability, metabolism, and excretion of key actives such as linalool and the impact of long-term repeated dosing. Such pharmacokinetic data can help correlate in vitro and clinical results ( 64 , 66 ).

Finally, lemon essential oil, the main component, D-limonene, boosts antimicrobial and antioxidant effects ( 15 , 67 , 68 ). However, further studies are needed on possible synergies with other components such as geranial ( 69 , 70 ). In addition, rigorous human clinical trials are required to validate efficacy as a natural food preservative and to determine optimal dosage ( 71 – 73 ). The effect on the gut microbiome is promising, but it is not yet clear what specific changes in bacterial composition drive the observed health outcomes ( 68 , 74 ).

14 Conclusion

Essential oils extracted from plants have been valued for their medicinal properties for centuries. Modern scientific research is now unraveling the composition and bioactivity of these complex natural extracts, providing insights into how essential oils might be used to help promote health and well-being. Based on the evidence summarized in the provided documents, several key conclusions regarding cinnamon, cilantro, cumin, parsley, lemon, orange, thyme, and rosemary essential oils can be drawn.

Firstly, these essential oils demonstrate varying degrees of antioxidant, antimicrobial, anti-inflammatory, or other beneficial biological effects. These effects are mediated by bioactive phytochemicals in the oils, such as cinnamaldehyde, linalool, limonene, thymol, and carnosic acid. The impacts of oils depend not just on their chemical composition but also on factors like genetics and growth conditions of the source plants. Standardization and quality control are thus important when studying and applying essential oil preparations. Secondly, many oils show promise as natural food preservatives—for example, inhibiting foodborne pathogens like Escherichia coli and Staphylococcus aureus . If efficacious and safe, plant-derived antimicrobials could replace synthetic additives. Areas needing more research include determining effects on food quality and nutritional content during storage.

Some of the main health benefits supported by current evidence are cinnamon oil improving glucose control and blood lipid levels; cilantro oil having parasite-killing properties; cumin oil reducing blood pressure; thyme oil protecting against oxidative cell damage and DNA mutations; and rosemary and thyme oils inhibiting cancer cell proliferation and viability. Further mechanisms of action are being elucidated—for instance, rosemary compounds may suppress altered metabolic pathways in tumor cells. More clinical trials are warranted to verify therapeutic efficacy and safety. An emerging area of research is how essential oil components like limonene and thymol influence intestinal microbiota populations.

So, essential oils are promising candidates for health promotion and disease treatment. However, converting traditional claims into evidence-based applications requires meticulous methodology. Key priorities in the future are clinical evaluations demonstrating efficacy, standardization, and quality control of oil preparations, untangling oils’ mechanisms of action, and further analyzing effects on human microbiota. With rigorous science illuminating their real therapeutic potential, essential oils could reveal themselves to be far more than just pleasant natural scents.

14.1 Limitations

This review is limited by the variability in the chemical composition of essential oils since these can vary according to the species/variety of the plant, growing conditions, time of harvest, extraction method, etc., making standardization and generalization of results difficult. Likewise, there is little information on the absorption, distribution, metabolism, and excretion (pharmacokinetics) of the components of essential oils in humans, and finally, there is not enough scientific evidence on interactions of essential oils with medications, nutrients, and other compounds - nutrient and drug interactions. For data analysis, the use of Cochrane tools to assess the risk of bias in randomized controlled trials, while for observational studies, the quality assessment tool of the US National Institutes of Health was not applied to the results since the included studies are in vitro .

Author contributions

CP-O: Conceptualization, Validation, Data curation, Investigation, Writing – original draft. FG: Conceptualization, Data curation, Investigation, Writing – original draft, Formal analysis, Methodology, Software. CM: Data curation, Formal analysis, Investigation, Methodology, Writing – review & editing. JM: Funding acquisition, Project administration, Supervision, Validation, Writing – review & editing. AO-M: Funding acquisition, Project administration, Supervision, Validation, Writing – review & editing, Conceptualization, Methodology.

The author(s) declare financial support was received for the research, authorship, and/or publication of this article. This study was supported by NovaVita S.A. grants for research. The funder was not involved in the study design, collection, analysis, interpretation of data, the writing of this article, or the decision to submit it for publication.

Acknowledgments

The authors would like to express their gratitude toward Mary Young and Tamara Packer for their interest in the research and support.

Conflict of interest

CP-O and JLM were employed by company NovaVita.

The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Publisher’s note

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

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Keywords: essential oils, nutrition, omics, bioactive compounds, well-being

Citation: Pezantes-Orellana C, German Bermúdez F, Matías De la Cruz C, Montalvo JL and Orellana-Manzano A (2024) Essential oils: a systematic review on revolutionizing health, nutrition, and omics for optimal well-being. Front. Med . 11:1337785. doi: 10.3389/fmed.2024.1337785

Received: 13 November 2023; Accepted: 25 January 2024; Published: 16 February 2024.

Reviewed by:

Copyright © 2024 Pezantes-Orellana, German Bermúdez, Matías De la Cruz, Montalvo and Orellana-Manzano. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY) . The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

*Correspondence: Andrea Orellana-Manzano, [email protected]

† These authors share first authorship

This article is part of the Research Topic

Holobiontic Epigenomic-Microbiomic-Metabolomic Perspectives of Diet and Nutrition towards Human Health

Aromatherapy and Essential Oils: A Map of the Evidence

• PMID: 31851445
• Bookshelf ID: NBK551017

Background: The purpose of this review is to provide the Veterans Health Administration (VHA) with a broad overview of the effectiveness of aromatherapy and essential oils (EOs), and the health conditions for which these interventions have been examined.

Data Sources and Study Selection: We searched multiple databases through February 2019 for systematic reviews (SRs) of aromatherapy and EOs for health conditions. Using pre-specified inclusion criteria, all abstracts and full-text articles were dual-screened for inclusion. When there were several qualified reviews for the same health condition, we selected a single review based on its recency, methods, scope, and applicability.

Data Abstraction: From each review, we abstracted the focus of the SR, the number of controlled trials included, combined number of participants, duration of trials, condition treated, and relevant findings from controlled trials. We abstracted separate data for each of 5 outcome categories: psychological outcomes, nausea/vomiting, pain and other physical outcomes, sleep outcomes, and global health outcomes.

Data Synthesis: For each review and outcome category we assigned values representing the effectiveness level of the intervention and confidence in the evidence and used these values to generate evidence maps. Additionally, we provide a narrative synthesis of the findings.

Results: We included 26 SRs representing the most recent and comprehensive evidence available. There is moderate-confidence evidence that aromatherapy is beneficial for pain in dysmenorrhea. Aromatherapy is potentially effective for pain in labor/childbirth; blood pressure reduction in hypertension; stress, depression, and sleep in hemodialysis patients; stress in healthy adults; anxiety in perioperative patients; and sleep quality in various populations, with low to moderate confidence in the evidence. For EOs applied topically, there is moderate confidence in the potentially positive effect of tea tree oil for tinea pedis. There is insufficient evidence of efficacy for all other conditions examined.

• Acknowledgments
• Executive Summary
• Introduction
• Summary and Discussion
• APPENDIX A. Search Strategies
• APPENDIX B. Study Selection
• APPENDIX C. Assessment of Confidence in the Evidence from Systematic Reviews of Aromatherapy and Essential Oils
• APPENDIX D. Peer Review Comments/Author Responses

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What Science Says About the Potential Healing Effects of Essential Oils

Essential oils smell great. but what do researchers have to say about the health benefits of essential oils are they really safe remedies for anxiety, stress, pain and other health problems.

This article was originally published on Feb. 18, 2020.

Since the dawn of civilization, people have turned to the power of plants for healing purposes. But one folk medicine in particular seems more popular than ever: essential oils.

Today, there’s renewed interest in using essential oils to improve physical or psychological well-being. One poll found that a third of Americans believe in the health benefits of essential oils and aromatherapy. No longer niche, these little vials of plant essence are a billion-dollar industry, favored by Gwyneth Paltrow and grandmas alike.

With around 90 essential oils on the market — each with its own purported healing qualities — there’s a so-called “cure” for practically everything. Lavender, sandalwood and bergamot are popular essential oils for stress relief. Varieties like ylang-ylang and jasmine are reputed to boost libido. Some, like lemon oil, are believed to address a laundry list of conditions: morning sickness, pain and acne, to name a few. But there’s a problem with essential oil claims: Science hasn’t caught up to their popularity.   There simply haven't been enough large-scale, peer-reviewed studies in humans to prove whether essential oils really can improve health or mood, or support any other commonly bragged about health benefits of essential oils.

With this in mind, let’s clear up what essential oils are, how they are thought to work, and what research says about them.

What's in Your Oils: Are Essential Oils Safe?

Essential oils are highly concentrated extracts of plant material — such as seeds, flowers, stems or roots.

But it can often be tough for consumers to know what they’re really buying. The market isn’t regulated, so there tends to be a lot of variation between essential oils — even among those that originate from the same brand.

“The constituent makeup of essential oils will vary from batch to batch, as they are drawn from plants that vary from country to country, field to field and even within the same plant from morning to evening,” says Mark Moss, a psychologist who studies essential oils at Northumbria University in the U.K., in an email to Discover . “The major components will always be there, but the relative concentration will vary.”

Another important thing to keep in mind is that essential oils haven’t been put through rigorous FDA testing and approval like the over-the-counter drugs available at your neighborhood pharmacy. So what essential oils do for health, if anything, is still pretty murky.

“Essential oils are neither medicines nor drugs because the effects have not been fully assessed yet in terms of science,” says Hideki Kashiwadani, a physiology researcher at Kagoshima University in Japan, in an email to Discover. 

Despite this, essential oils have wide appeal, particularly among people who have grown dissatisfied with modern Western medicine . And this alternative therapy is showing no signs of slowing down.

How Essential Oils are Used 

Most essential oils are inhaled via diffusion or applied topically to the skin after being mixed with a carrier oil. Other essential oils are supposed to be ingested, but medical professionals and health authorities generally warn against the safety of this method. 

When essential oils are inhaled via aromatherapy, compounds are absorbed through receptors in our noses , which send messages to our olfactory system, the part of the brain responsible for our sense of smell. Eventually, these messages reach other areas of the brain, such as the limbic system, which plays a role in our emotions. 

Read more : The Sense of Smell in Humans is More Powerful Than We Think

When essential oils are applied topically for cosmetic reasons or to treat aches and pains, the compounds are absorbed into the skin and eventually enter the bloodstream before they’re metabolized by the liver. 

But beyond that, even scientists have a tough time figuring out what various essential oils really do. Since there are no accepted standards for essential oils, Kashiwadani explains that scientists often find it challenging to replicate another scientist’s experiment.   

“One of the problems with essential oils and the lack of standardization is that you can’t tell if two researchers are actually testing the same essential oil,” Moss says.

But other issues — which are surprisingly commonplace in scientific research — further complicate matters. For instance, human studies on essential oils are few and far between. Of the research that has been conducted on humans, many studies involved small numbers of participants, which can skew results. As a rule of thumb, reviews or meta-reviews, which draw conclusions from large numbers of similar studies, tend to be the most reliable and comprehensive.

We also must remember that correlation does not equal causation. In other words, a mere association between two things isn't enough to prove a direct cause-and-effect relationship. So, even if a study found people who smelled lavender aroma felt less anxious, something else may be responsible for the effect (such as controlled breathing).

On top of that, the results from scientific studies can sometime be misinterpreted or blown out of proportion. When scientists study treatments, they’re looking for changes that are "statistically significant." All this means is that the results cannot be explained by random chance alone. So the impact of an essential oil might be scientifically significant, but fall far short of what we might view as meaningful.

In light of the shortcomings of essential oil studies, a lot of the information concerning the health benefits of essential oils tends to be anecdotal or rooted in folklore. And their safety hasn’t been fully vetted. So it’s important for people to remember that natural or organic doesn’t directly translate to being “safe” or “beneficial.” Plant compounds — especially in high doses — can be toxic, irritating or may cause allergic reactions or drug interactions.

What Are the Health Benefits of Essential Oils?

But essential oils may not be totally worthless. Based on his own work, Moss said rosemary, sage and peppermint oils might improve memory and cognition to a degree. He also says lavender has been linked with improved sleep. Just don't expect essential oils to be magical elixirs. They're a far cry from being medication, and shouldn't replace standard medical care.

“The effects of essential oils are small. They are not a panacea. They can provide small benefits for individuals and should, in my opinion, be seen as self-care life enhancers rather than treatments as such,” Moss said.

If anything, many essential oils smell nice. So, if spritzing your pillow with lavender oil brings enjoyment and relaxation — even via the placebo effect — is there really anything wrong with that?  

“Don’t go searching for solutions to problems. Consider the potential for enjoying the experience. That is a benefit in itself,” Moss said.

Read more : The Power of the Placebo

Essential Oils as ‘Medicine’

Are essential oils safe and effective treatments for certain medical conditions? The jury's still out, but Discover rounded up some of the published work that explores the effects of some popular essential oils in animals and humans. If you’re thinking about trying essential oils, make sure you check with your doctor first.

Rosemary Oil

The woodsy aroma of rosemary may do more than perk up a roast chicken. A small study of 20 people from Moss’ research team at Northumbria University linked rosemary to improved memory and cognition , particularly among older adults.

Another small study from Moss' team found that rosemary might improve test scores among school-aged kids. Children who took tests in rooms scented with rosemary received higher scores than children in nonscented rooms.

Despite his work investigating rosemary, Moss said he's not necessarily an advocate of promoting the use of essential oils, but thinks consumers should be able to make their own choices.

Lavender Oil

Lavender is one of the most popular scents in aromatherapy. Studies in both mice and horses have found that the scent of lavender is calming. In humans, small-scale studies found that it might have a modest effect on anxiety.

One study of 100 people found that lavender slightly improved anxiety before surgery. The researchers cautioned, however, that additional research is needed before drawing conclusions between lavender aroma and anxiety.

Taking lavender oil capsules orally might also have some effect on anxiety. That's according to a meta-analysis of five studies that involved more than 500 people , which looked at how lavender capsules measured up to a placebo and some anti-anxiety drugs. Although lavender capsules (also known as silexan) helped with anxiety, it also caused unpleasant side effects like nausea, belching and diarrhea in some people.

Lavender is also a common sleep aid. A review of studies concluded that it may offer some small to moderate sleep-promoting benefits. However, the review called for larger and more rigorous studies that investigate lavender and sleep.

Beyond that, lavender may have some pro-social benefits . A study that involved 90 people found that the aroma of lavender was more effective than a control in promoting a sense of trust among strangers.

But lavender oil maybe isn’t a good idea for everyone. It may be a hormone disrupter, and studies have linked regular exposure to lavender oil with abnormal breast growth in girls . Lavender (and tea tree oil) was also found to cause abnormal breast tissue growth in boys .  

Peppermint Oil

Peppermint oil, which may have pain-relieving qualities, has been used for centuries to treat gastrointestinal problems . But unlike some other essential oils, there's pretty sound evidence to back up these claims. Reviews of studies have found that taking peppermint oil capsules may ease irritable bowel syndrome symptoms, like gastrointestinal pain.

A small pilot study also found that peppermint oil capsules may be helpful for people who have problems swallowing during meals or experience noncardiac chest pains. Consuming peppermint tablets helped ease discomfort in these patients, likely because the compounds helped to relax smooth muscles in the lower esophagus.

Tea Tree Oil

Tea tree oil is often found in cosmetic products because of its purported anti-microbial and anti-inflammatory properties. When applied to the skin, tea tree oil might be an effective treatment for mild to moderate acne .

A review study found tea tree oil was better than placebos, and just as effective as benzoyl peroxide, in stopping pimples. In addition to acne, several older studies suggest tea tree oil may be helpful for nail fungus and athlete’s foot.

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Home > Books > Essential Oils - Recent Advances, New Perspectives and Applications

Essential Oils and Their Bioactive Molecules: Recent Advances and New Applications

Submitted: 27 September 2023 Reviewed: 10 October 2023 Published: 14 February 2024

DOI: 10.5772/intechopen.113406

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This chapter explores the latest advancements and applications of essential oils, focusing on evidence-based research and practical insights. Beginning with an introduction to essential oils’ historical significance, it outlines recent breakthroughs in research, novel extraction techniques, and advancements in understanding their chemical composition. New perspectives on essential oil use are explored, including their potential to promote mental well-being, applications in environmental practices, and emerging industry trends. The chapter highlights innovative applications, such as aromatherapy, skincare, and culinary arts. In healthcare, evidence-based applications and research on antimicrobial properties and pain management are discussed. Real-world case studies demonstrate essential oils’ impact across various industries. The chapter also addresses challenges, including safety, ethics, and regulatory considerations. Future research opportunities are identified, emphasizing essential oils’ potential in cutting-edge fields like nanotechnology and biomedicine. In conclusion, essential oils offer a rich source of health and innovation, bridging traditional knowledge with modern advancements. Their significance in diverse applications invites further exploration and utilization to unlock their full potential.

• essential oils
• recent advances
• applications

Author Information

Guedri mkaddem mounira *.

• Laboratory of Energy, Water, Environment and Process, (LR18ES35), National Engineering School of Gabes, University of Gabes, Gabes Tunisia

*Address all correspondence to: [email protected]

1. Introduction

Essential oils have played a captivating and vital role in human history, entwining nature’s essence with the pursuit of well-being and healing. Derived from aromatic plants through intricate extraction processes, these precious oils have been prized for their therapeutic properties and cultural significance since ancient times [ 1 ]. In this chapter, we embark on an enlightening journey to explore the evolving world of essential oils and their remarkable impact on various aspects of our lives.

Essential oils are volatile, aromatic compounds obtained from different parts of plants, including flowers, leaves, stems, and roots. These oils are the pure essence of the plant, capturing its unique fragrance and potent bioactive compounds [ 2 ]. Through the ages, essential oils have been revered for their diverse applications, ranging from medicinal practices and religious rituals to perfumery and culinary arts. The ancient civilizations of Egypt, Greece, and China harnessed their therapeutic properties, recognizing the power of nature in promoting physical and emotional well-being [ 3 ].

Drawing inspiration from our rich historical tapestry, this chapter aims to shed light on the contemporary understanding and advancements surrounding essential oils. We delve into the latest scientific research and cutting-edge technologies that have deepened our comprehension of these natural wonders. Moreover, we explore novel perspectives that have emerged, unveiling innovative applications that extend beyond traditional boundaries [ 4 ].

This chapter is divided into several sections, each meticulously created to offer a comprehensive exploration of essential oils in the modern world. We begin by examining recent advances in essential oil research, uncovering groundbreaking studies that have unveiled new insights into their chemical composition and extraction techniques. These discoveries pave the way for exciting possibilities in utilizing essential oils across various domains.

Next, we delve into new perspectives surrounding essential oil use, focusing on their potential to foster mental well-being, support sustainable agricultural practices, and spearhead new trends in the ever-evolving essential oil industry.

In the subsequent sections, we turn our attention to the diverse applications of essential oils. We explore their role in aromatherapy and skincare, where they are increasingly recognized for their therapeutic and cosmetic benefits. Additionally, we venture into the culinary realm, where essential oils infuse dishes with unique and enticing flavors, redefining gastronomic experiences.

Furthermore, we examine the growing influence of essential oils in healthcare, where traditional and alternative medicine converge. From antimicrobial properties to pain management, essential oils are paving the way for complementary therapies that embrace the synergy of nature and science.

The chapter also highlights real-world applications of essential oils through compelling case studies, illuminating their successful integration across various industries and contexts. It also addresses challenges surrounding the responsible use of essential oils, including safety considerations, ethical sourcing, and regulatory aspects.

Lastly, we glimpse into the future, identifying promising research opportunities and potential for essential oils to revolutionize fields like nanotechnology and biomedicine.

By the chapter’s end, readers will gain a profound appreciation for essential oils’ enduring allure and their boundless potential in shaping the present and transforming the future.

2. Recent advances in essential oil research

The realm of essential oil research has witnessed an extraordinary surge of interest in recent years, leading to remarkable discoveries and groundbreaking advancements. This section investigates the dynamic landscape of contemporary essential oil research, highlighting the latest scientific studies, innovative extraction techniques, and deeper insights into the chemical composition of these nature-derived treasures.

2.1 Overview of recent scientific studies and breakthroughs

Research on Antimicrobial Properties: Studies exploring the antimicrobial efficacy of essential oils against bacteria, viruses, and fungi have yielded promising results. For instance, research by Blejan et al. [ 6 ] demonstrated the potent antimicrobial actions of tea tree oil, oregano oil, and lavender oil, raising possibilities for novel treatments against drug-resistant pathogens [ 7 ].

Neurological Effects and Mood Regulation: Scientific interest in essential oils’ impact on the nervous system has surged, with investigations into their potential to alleviate stress, anxiety, and depression. Certain oils, like bergamot and frankincense, have shown modulating effects on neurotransmitters, shedding light on their potential role in mental well-being [ 10 , 11 ].

Anti-Inflammatory and Analgesic Properties: The anti-inflammatory and analgesic properties of essential oils have attracted attention in pain management and inflammatory disorders [ 8 ]. However, promising anti-inflammatory effects of peppermint, eucalyptus, and ginger oils in preclinical models [ 9 ].

Recent advancements in essential oil research.

2.2 Novel extraction methods and technologies

Supercritical Fluid Extraction (SFE): Supercritical carbon dioxide (CO 2 ) extraction has gained popularity due to its ability to yield high-quality essential oils without leaving behind harmful residues. SFE allows for precise control of temperature and pressure, preserving the delicate aromatic compounds of the plant material [ 15 ].

Enzyme-Assisted Extraction: Enzyme-assisted extraction techniques have emerged as eco-friendly alternatives. Enzymes facilitate the breakdown of plant cell walls, enhancing the release of essential oil compounds and increasing extraction yields [ 16 ].

Microwave-Assisted Extraction (MAE): MAE employs microwave energy to accelerate the extraction process, reducing extraction times and energy consumption while maintaining the integrity of the essential oil constituents [ 17 ].

2.3 Advancements in understanding the chemical composition of essential oils

Identification of Bioactive Compounds: Researchers have identified numerous bioactive compounds present in essential oils, such as terpenes, phenols, and aldehydes. Understanding the roles of these compounds in conferring therapeutic properties has paved the way for targeted applications [ 18 ].

Synergy and Entourage Effect: Studies have highlighted the importance of the synergy between various components within essential oils. The entourage effect, where the combined action of multiple compounds enhances therapeutic efficacy, has been observed in certain oils [ 19 ].

In conclusion, recent advances in essential oil research have catapulted these natural aromatic substances into a realm of scientific exploration, paving the way for novel applications in various fields. From antimicrobial potential to mental health support and innovative extraction techniques, essential oils continue to captivate researchers and enthusiasts alike, forging a path toward a deeper understanding of their multifaceted properties.

3. Exploring new perspectives in essential oil use

In this section, we embark on a journey to discover the captivating role of essential oils in enhancing mental well-being, their potential applications in environmental and agricultural practices, and the exciting emerging trends and opportunities within the essential oil industry.

3.1 The role of essential oils in promoting mental well-being and stress reduction

The enchanting scents of essential oils have long been celebrated for their profound impact on mental health and emotional balance. Numerous studies have shown that inhaling certain essential oils can activate the olfactory system, triggering the release of neurochemicals that influence our mood and emotions [ 20 , 21 ]. Lavender, for example, has been found to reduce anxiety and promote relaxation [ 22 ], while citrus-based oils like bergamot and sweet orange have uplifting effects on mood [ 23 , 24 ].

Moreover, essential oils can be used in aromatherapy, a holistic practice that involves inhaling or applying oils to the skin to improve psychological and physical well-being [ 25 ]. Aromatherapy has gained popularity as a complementary therapy in various healthcare settings, such as hospitals, hospices, and wellness centers [ 26 ]. Its stress-reducing and mood-enhancing properties have also been beneficial for managing stress-related conditions like depression and anxiety [ 27 ].

3.2 Potential applications of essential oils in environmental and agricultural practices

The versatility of essential oils extends beyond their impact on human health; they also hold great potential in environmental and agricultural practices. Many essential oils possess natural insecticidal and repellent properties that can be harnessed to manage pests in a sustainable manner [ 28 ]. For instance, eucalyptus oil has demonstrated insecticidal effects against several insect species [ 29 ]. By incorporating essential oils into integrated pest management strategies, farmers can reduce reliance on chemical pesticides, mitigating environmental harm and promoting ecological balance [ 30 ].

Furthermore, some essential oils have shown promise in enhancing soil health and stimulating plant growth. Studies have indicated that certain oils, such as peppermint and cinnamon, possess plant growth-promoting properties [ 31 , 32 ]. Their application in agriculture can lead to improved crop yields and reduced dependence on synthetic fertilizers, thereby contributing to sustainable and eco-friendly farming practices.

3.3 Emerging trends and opportunities in the essential oil industry

The essential oil industry has witnessed remarkable growth in recent years, driven by the increasing demand for natural and holistic approaches to health and well-being. Entrepreneurs and businesses are capitalizing on this trend by exploring innovative ways to incorporate essential oils into various products. From skincare and personal care items to household cleaners and aromatherapy diffusers, essential oils are finding diverse applications [ 33 ].

Advancements in technology and distillation techniques have also contributed to the growth of the industry. New extraction methods, such as supercritical fluid extraction and microwave-assisted extraction, are being explored to improve the efficiency and quality of essential oil production [ 34 , 35 ].

Additionally, the rise of e-commerce and digital marketing platforms has enabled small-scale distilleries and artisanal producers to reach a broader customer base, fostering a more inclusive and competitive market.

As we continue to explore the alluring world of essential oils, it becomes evident that their impact reaches far beyond the confines of aromas and scents. From promoting mental well-being to revolutionizing environmental practices and driving industry trends, essential oils stand as a testament to the power of nature’s bounty. Their potential knows no bounds, and we eagerly await the exciting innovations that lie ahead.

4. Essential oils in healthcare

In this section, we explore the multifaceted applications of essential oils in healthcare, ranging from evidence-based practices in traditional and alternative medicine to their role in antimicrobial treatments and pain management.

4.1 Evidence-based applications in traditional and alternative medicine

Essential oils have been used for therapeutic purposes across cultures and traditions for centuries. In recent years, scientific research has shed light on the efficacy of these aromatic wonders in traditional and alternative medicine practices.

A prime example of their effectiveness is in aromatherapy, a complementary therapy that harnesses the aromatic properties of essential oils to promote healing and well-being. Several studies have demonstrated the benefits of aromatherapy in managing anxiety, depression, and stress-related conditions [ 27 ]. Furthermore, aromatherapy has been incorporated into healthcare settings, such as hospitals and palliative care facilities, to enhance patient comfort and reduce the need for conventional medications [ 36 ].

The evidence supporting the use of essential oils in traditional medicine is continually growing, encouraging further exploration into their therapeutic potential.

4.2 Current research on the antimicrobial properties of essential oils

In the face of growing antimicrobial resistance, essential oils have emerged as a promising area of research for their potential as natural antimicrobial agents. Many essential oils exhibit broad-spectrum antimicrobial properties, capable of combating a wide range of bacteria, viruses, and fungi.

Tea tree oil, for instance, has demonstrated significant antimicrobial effects against various strains of bacteria and fungi [ 37 ]. Oregano oil is also known for its potent antibacterial and antifungal properties [ 38 ].

Current research is focusing on understanding the mechanisms behind these antimicrobial activities and exploring the potential use of essential oils in developing alternative treatments to combat infectious diseases. However, it is important to note that further investigation is required to determine their safety and efficacy for use in medical settings.

4.3 The role of essential oils in pain management and complementary therapies

Pain management remains a significant challenge in healthcare, and essential oils have emerged as a complementary approach to address pain and discomfort. The analgesic and anti-inflammatory properties of certain essential oils offer promising alternatives to conventional pain medications.

For example, peppermint oil has been found to alleviate headaches and migraines [ 39 ], while lavender oil has been shown to reduce labor pain in pregnant women [ 40 ]. In palliative care, essential oils, such as frankincense and chamomile, have been used to alleviate symptoms and provide comfort to patients with chronic pain and terminal illnesses [ 41 ].

Complementary therapies that incorporate essential oils, such as massage and aromatherapy, have gained popularity for their ability to reduce pain, enhance relaxation, and improve overall well-being [ 42 ].

As research in this area progresses, essential oils hold the promise of becoming valuable tools in integrated pain management approaches.

As we delve into the realms of essential oils in healthcare, we are reminded of their enduring presence in traditional medicine, their potential as antimicrobial warriors, and their gentle touch in pain management. Through evidence-based practices and ongoing research, essential oils continue to carve a place in modern healthcare as aromatic allies in the pursuit of wellness ( Figure 1 ).

Diverse applications of essential oils in modern industries.

5. Case studies: real-world applications

In the captivating world of essential oils, success stories and case studies abound, showcasing the remarkable impact these aromatic wonders have had across various industries. In this section, we delve into practical examples of essential oil integration, highlighting specific success stories that demonstrate the diverse and innovative applications of these botanical extracts.

5.1 Enhancing wellness in healthcare facilities

Essential oils have found their way into healthcare settings, offering a holistic approach to patient care and well-being. In a case study conducted at a hospital’s palliative care unit [ 41 ], aromatherapy using essential oils like lavender, chamomile, and frankincense was implemented to alleviate pain and provide comfort to patients with chronic conditions. The results demonstrated a significant reduction in reported pain levels and an improvement in the overall well-being of patients, displaying the potential of essential oils to enhance the healthcare experience.

5.2 Creating natural and sustainable cleaning solutions

In the commercial and cleaning industry, essential oils have emerged as a viable alternative to conventional chemical-based products. A case study conducted in a hotel chain [ 43 ] demonstrated the successful implementation of essential oils in cleaning solutions. Citrus-based oils, such as lemon and orange, were used to create natural and effective multi-purpose cleaners. This eco-friendly approach not only reduced the hotel’s environmental footprint but also enhanced the guest experience by eliminating harsh chemical odors.

5.3 Revolutionizing personal care and beauty products

The beauty and personal care industry has witnessed a revolution with the integration of essential oils into various products. In a case study focusing on a natural skincare brand [ 44 ], essential oils like rosehip seed oil and chamomile were used in the formulation of anti-aging serums and facial oils. The results showed improvements in skin texture and hydration, proving the efficacy of essential oils in promoting healthy and radiant skin.

5.4 Improving productivity and employee well-being in the workplace

In the corporate world, essential oils have been embraced to create a more productive and stress-free work environment. In a case study conducted at a technology company [ 45 ], diffusers with essential oils like peppermint and eucalyptus were strategically placed in common areas and workspaces. This implementation resulted in increased focus and reduced stress levels among employees, ultimately improving workplace morale and productivity.

5.5 Sustainable agriculture and pest management

The agricultural sector has also reaped the benefits of essential oils in sustainable pest management. In a case study, focusing on organic farming practices [ 46 ], essential oils like neem oil and thyme oil were integrated into pest control strategies. These natural alternatives effectively reduced pest infestations and crop damage, promoting environmentally friendly and economically viable farming practices.

These case studies serve as a testament to the wide-ranging applications of essential oils, spanning from healthcare to agriculture and beyond. Their integration into various industries not only displays their versatility but also emphasizes the significance of sustainable and natural solutions in today’s world.

6. Addressing challenges in essential oil applications

As the popularity of essential oils continues to soar, so do the challenges associated with their widespread applications. In this section, we explore the crucial aspects of potential safety concerns, sustainability and ethical sourcing issues, and the importance of regulatory considerations and standardization.

6.1 Potential safety concerns and precautions

While essential oils offer numerous benefits, it is essential to recognize that their concentrated nature can pose safety risks if not used properly. Some essential oils may cause skin irritation or allergic reactions in certain individuals and others may interact with medications [ 47 ]. To address these concerns, it is crucial to practice responsible use and adhere to recommended dilution guidelines.

Ingestion of essential oils is a particularly contentious issue, as some oils can be toxic when taken internally [ 48 ]. Professional guidance from trained aromatherapists or healthcare practitioners is advised before internal use. Additionally, essential oils should be kept out of reach of children and pets to prevent accidental ingestion or exposure.

6.2 Issues related to sustainability and ethical sourcing

The demand for essential oils has led to challenges in sustainability and ethical sourcing. Some essential oil-producing plants are at risk of overharvesting, endangering both the plant species and the communities dependent on them for livelihoods [ 49 ]. Unregulated harvesting practices can contribute to deforestation, habitat destruction, and loss of biodiversity.

To address these issues, sustainable and ethical sourcing practices are becoming increasingly vital in the essential oil industry. Initiatives such as fair trade partnerships, responsible cultivation, and wild-harvesting certifications are essential for ensuring that essential oils are sourced responsibly and that the ecosystems and communities involved are protected.

6.3 Regulatory considerations and standardization

The lack of consistent regulations and standardization in the essential oil industry can be a significant challenge. Different countries and regions may have varying guidelines regarding the production, labeling, and marketing of essential oils, leading to confusion among consumers and potential quality issues.

To address this concern, efforts are being made to establish industry standards and certifications. Organizations such as the International Organization for Standardization (ISO) and the European Medicines Agency (EMA) are working to create guidelines for essential oil quality, purity, and safety [ 47 ]. Seeking essential oils from reputable and transparent suppliers who adhere to these standards can help ensure product integrity and consumer confidence.

As the use of essential oils continues to evolve, it is imperative to address these challenges to ensure the safety, sustainability, and efficacy of their applications. Responsible use, ethical sourcing, and adherence to quality standards are crucial steps toward harnessing the full potential of essential oils while preserving the well-being of both individuals and the environment.

7. Future directions and research opportunities

In this section, we aim to illuminate the potential for essential oils to shape the future of various industries and fields, from healthcare and agriculture to nanotechnology and beyond. Through a forward-looking lens, we uncover new perspectives and explore the uncharted territories where essential oils could revolutionize science, enhance well-being, and inspire transformative applications for generations to come.

7.1 Promising areas for further research and development

Novel Extraction Techniques: The future of essential oil research lies in exploring and developing innovative extraction methods. Techniques such as supercritical fluid extraction (SFE), microwave-assisted extraction (MAE), and ultrasound-assisted extraction (UAE) have shown promise in enhancing the yield and purity of essential oils [ 50 , 51 ].

Chemical Composition and Standardization: To unlock the full potential of essential oils, it is crucial to delve deeper into their chemical composition. Comprehensive studies on the complete chemical profile of essential oils will aid in standardization and quality control procedures [ 52 ].

Synergistic Effects and Combinations: Investigating the synergistic effects of combining different essential oils or integrating them with other natural compounds is an exciting area for future exploration. Understanding these interactions can lead to the formulation of more potent and tailored therapeutic blends [ 53 ].

Mechanisms of Action: Unraveling the molecular and cellular mechanisms of action of essential oils is a key research avenue. Studies in this area will shed light on how essential oils interact with biological systems and pave the way for the development of new therapies and medicines [ 53 ].

Safety and Toxicology: In-depth safety and toxicology studies are essential to establish evidence-based guidelines for the safe use of essential oils in various applications. Identifying appropriate dosages and potential adverse effects will be crucial for ensuring their safe integration into healthcare practices [ 9 ].

Bioavailability Enhancement: Enhancing the bioavailability of essential oil compounds is a promising research direction. Developing innovative encapsulation techniques or novel formulation strategies can optimize the absorption and distribution of essential oil components within the body [ 54 ].

7.2 The potential of essential oils in cutting-edge fields

Nanotechnology Applications: Essential oils hold tremendous potential in the field of nanotechnology. Integrating essential oils into nanocarriers can revolutionize targeted drug delivery systems, especially for cancer treatment and chronic diseases [ 53 ].

Biomedicine and Healthcare: The antimicrobial, anti-inflammatory, and antioxidant properties of essential oils offer exciting prospects in biomedicine. Integrating essential oils as adjunct therapies in conventional medicine could enhance treatment outcomes and patient well-being [ 55 ].

Neurological Disorders: Exploring the effects of essential oils on neurological disorders, such as Alzheimer’s and Parkinson’s diseases, is a promising area. Studies suggest that essential oils may improve cognitive function and reduce neuroinflammation [ 56 ].

Antimicrobial Resistance: Essential oils may serve as alternative antimicrobial agents to combat the global challenge of antimicrobial resistance. Their potent antimicrobial activity against various pathogens warrants further investigation [ 55 ].

Environmental Applications: Essential oils can play a crucial role in developing eco-friendly products such as natural pesticides, insect repellents, and cleaning agents. This research direction aligns with the growing demand for sustainable and environmentally friendly solutions [ 57 , 58 ].

Food Preservation: Essential oils’ potential as natural preservatives for extending the shelf life of food products and inhibiting foodborne pathogens holds promise for the food industry [ 59 , 60 ].

By focusing on these promising areas for research and displaying the potential of essential oils in cutting-edge fields, we can pave the way for new discoveries, innovations, and applications that will undoubtedly shape the future of essential oil science and industry.

8. Conclusion

In this chapter, we have explored the recent advances, new perspectives, and applications of essential oils, uncovering a myriad of exciting possibilities for their integration into modern research and practices. Throughout the discussion, several key findings and insights have emerged, underscoring the immense potential of essential oils across various domains.

Firstly, we have witnessed the emergence of novel extraction techniques such as supercritical fluid extraction (SFE), microwave-assisted extraction (MAE), and ultrasound-assisted extraction (UAE), which hold promise in enhancing the yield and purity of essential oils [ 15 , 17 , 51 ]. These advancements pave the way for more sustainable and efficient production methods, ensuring the availability of high-quality essential oils for diverse applications.

Moreover, comprehensive studies on the chemical composition of essential oils have shed light on their diverse and intricate profiles, allowing for standardization and quality control measures [ 18 ]. This knowledge is vital in ensuring consistent therapeutic properties and safety, further fueling the growth of essential oils’ integration into healthcare practices and other industries.

The exploration of synergistic effects and combinations of essential oils has opened new avenues for developing targeted therapeutic blends [ 61 , 62 ]. Understanding how essential oils interact with biological systems at the molecular and cellular levels has provided crucial insights into their mechanisms of action [ 63 ], presenting exciting prospects for the development of novel therapies and medicines.

As we continue to harness the potential of essential oils, it is essential to address safety concerns and establish evidence-based guidelines for their use [ 9 ]. By doing so, we can confidently integrate essential oils into diverse applications while ensuring the well-being of individuals and the environment.

In exploring the future directions and research opportunities, we have identified cutting-edge fields where essential oils can make a significant impact. Integrating essential oils with nanotechnology holds the potential to revolutionize targeted drug delivery, presenting opportunities for more effective and precise treatments [ 64 ]. Additionally, essential oils’ application in biomedicine and healthcare has the potential to augment conventional therapies, improving patient outcomes and overall well-being [ 65 , 66 ].

The prospects of essential oils in neurological disorders, antimicrobial resistance, environmental applications, and food preservation demonstrate their versatile and wide-ranging capabilities [ 56 , 57 , 58 , 59 , 60 ]. These applications align with the growing demand for sustainable and natural solutions, emphasizing the significance of essential oils in shaping a healthier and more environmentally conscious future.

In conclusion, essential oils represent a vast reservoir of natural compounds with extraordinary potential. From ancient traditional uses to cutting-edge scientific applications, their journey has been one of continuous discovery and innovation. As we forge ahead in the realm of essential oil research and development, it is evident that these aromatic extracts will play a pivotal role in modern applications, revolutionizing various industries and enriching human well-being.

By embracing this fusion of traditional wisdom and modern science, we can unlock the full potential of essential oils and foster a future where nature’s gifts are harnessed responsibly for the betterment of society.

Conflict of interest

The authors declare no conflict of interest.

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Aromatherapy

Aromatherapy is the use of essential oils from plants (flowers, herbs, or trees) as a complementary health approach. The essential oils are most often used by inhaling them or by applying a diluted form to the skin. Many essential oils are used in aromatherapy, including those from Roman chamomile, geranium, lavender, tea tree, lemon, ginger, cedarwood, and bergamot.

Aromatherapy is sometimes used for insomnia, but we don’t know whether it’s helpful because little rigorous research has been done on this topic.

Aromatherapy is sometimes incorporated into massage therapy for various conditions, such as knee pain from osteoarthritis or pain, anxiety, and other symptoms in people with cancer.

One study of aromatherapy using two contrasting scents, lemon and lavender, in people under stress found that lemon had a positive effect on mood but neither scent affected stress indicators, biochemical markers of immune system changes, or pain control.

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• Published: 13 January 2021

A pilot study on essential oil aroma stimulation for enhancing slow-wave EEG in sleeping brain

• Li-Wei Ko 1 , 2 , 3 ,
• Cheng-Hua Su 1 , 2 ,
• Meng-Hsun Yang 2 ,
• Shen-Yi Liu 4 &
• Tung-Ping Su 5 , 6  

Scientific Reports volume  11 , Article number:  1078 ( 2021 ) Cite this article

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• Neuroscience

Sleep quality is important to health and life quality. Lack of sleep can lead to a variety of health issues and reduce in daytime function. Recent study by Fultz et al. also indicated that sleep is crucial to brain metabolism. Delta power in sleep EEG often indicates good sleep quality while alpha power usually indicates sleep interruptions and poor sleep quality. Essential oil has been speculated to improve sleep quality. Previous studies also suggest essential oil aroma may affect human brain activity when applied awake. However, those studies were often not blinded, which makes the effectiveness and mechanism of aroma a heavily debated topic. In this study, we aim to explore the effect of essential oil aroma on human sleep quality and sleep EEG in a single-blinded setup. The aroma was released when the participants are asleep, which kept the influence of psychological expectation to the minimum. We recruited nine young, healthy participants with regular lifestyle and no sleep problem. All participants reported better sleep quality and more daytime vigorous after exposing to lavender aroma in sleep. We also observed that upon lavender aroma releases, alpha wave in wake stage was reduced while delta wave in slow-wave sleep (SWS) was increased. Lastly, we found that lavender oil promote occurrence of SWS. Overall, our study results show that essential oil aroma can be used to promote both subjective and objective sleep quality in healthy human subjects. This makes aroma intervention a potential solution for poor sleep quality and insomnia.

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Introduction.

Sleep is one of the most fundamental physical requirements for human survival, and increasingly viewed as playing an important role in restitution of human body 1 . An important aspect of well-being, sleep quality is closely related to overall quality of life, secretion of the stress hormone, cortisol, and immunity 2 . On the other hand, sleep deprivation is prevalent in modern society. Lack of sleep is known to contribute to a wide range of physical and mental health issues including impaired immunity 3 , memory loss 4 , obesity 5 , 6 , increased risk of cardiovascular disorder 7 , and more. Although sleep quality can be improved by hypnotics, like benzodiazepines and zolpidem, these medications can lead to other issues including sleep walking 8 , memory loss 9 , and impaired cognitive function 10 .

It’s long speculated that essential oils from some plants may help improve sleep quality, either through inhaling or applying on skin. One of the most commonly used essential oil is lavender oil, which has been found to improve sleep quality and mood 11 , 12 , 13 , 14 , 15 . However, the mechanism behind various oil’s effect on human brain was not well explored. Therapies and interventions involving aroma has not been accepted by mainstream science and are often considered pseudoscience. One of the issues withholding research on aroma is that designing a blinded experiment for aroma inhalation is hard. It’s difficult to find an innocuous placebo that shares a similar smell with the aroma of interest 16 . As such, subjects are often not blinded in previous studies. What’s worse, most studies on aroma were heavily focused on behavioral changes, which make their results even more susceptible to participants' perceptions and expectations. While Chien et al. 13 demonstrated in their study that lavender oil helped reduce insomnia, Howard and Hughes’ study 17 suggested that psychological expectations may have more effect than the aroma itself. Without further understanding on mechanisms of essential oil aroma, it is hard to evaluate its effectiveness and improve the efficiency of its application. Alternatively, neuroimaging technology like electroencephalography (EEG) could provide a more objective insight into aroma’s effect than behavioral studies. An additional benefit of EEG is that it can be performed when the subject is unconscious. Conducting aroma study in sleep time would exempt the need to find a similar smelling placebo and keep the influence of subject expectancy to minimal. Therefore, EEG could be an effective method in studying effects of aroma intervention on human sleep and human brain in general.

Sleep EEG has an episodic variation that can be divided into different stages by trained technicians 18 , 19 . According to guideline provided by American Academy of Sleep Medicine (AASM), these stages include wake (W), non-rapid eye movement (NREM) stage 1 (N1), NREM stage 2 (N2), NREM stage 3 (N3), and rapid eye movement (REM) 20 . These stages can be identified through polysomnography (PSG), which is commonly used to record various bio-signals like EEG, heart rate, nasal air flow and body positions during sleep. The wake stage is dominated by alpha wave (8–12 Hz) activity in the brain and indicates brief interruption of sleep, of which the person may or may not be aware. The N1, N2, and REM stage are regarded as light sleep during which brain waves slow down, but the person is still easy to wake. N3 is dominated by slower delta wave (0.5–4 Hz) activity, which gives it the alternative name “slow-wave sleep” (SWS). Frequent occurrences of wake stage and increased alpha wave activity usually indicate poor sleep quality, while increased N3 and delta wave activity reflects good sleep quality 21 , 22 . Recent study by Fultz et al. 23 also suggested that SWS is crucial to cerebrospinal fluid (CSF) flow and removal of toxic materials from brain. Previous study done by Goel et al. 11 found that inhaling lavender aroma before sleep could increase SWS and subjective sleep quality. Other studies also reported that inhaling lavender aroma increases theta (4-7 Hz) wave 24 , 25 throughout the whole brain during waking times. These studies suggest that lavender aroma may promote low-frequency (theta & delta) brain waves, which could increase deep sleep and improve individual sleep quality. In this study, we present a single-blinded approach to explore inhaled essential oil aroma’s effect on human sleep. We recruited healthy people as a proof of concept to see how aroma may affect sleep stages, sleeping brain activity, and overall sleep quality.

Participants

Nine healthy, right-handed volunteers participated in this study (four females and five males; overall mean age 22 ± 2 years; males: 21.5 ± 0.5 years; females: 22.8 ± 3 years). All participants were asked to keep a regular daily routine and filled out their daily sleep schedules for 1 week before the experiment. All participants gave clear, informed written consent before participating the experiment. None of the participants reported having any smell disorder, relevant history of medications used, smoking, nasal allergies, night shifts or slept during daytime within the previous month. The experiment and methodology were vetted and approved by the Institutional Review Board (IRB) of National Chiao Tung University. All experimental methods follow the guideline of Taiwan Society of Sleep Medicine (TSSM) 26 and were performed in accordance with local legal regulation.

Sleep laboratory

The sleep laboratory was designed based on a typical home bedroom to provide a comfortable environment for participants. The sleep laboratory was divided into two parts: an experimental room and a monitoring room. The experimental room had a bed with sheets and pillow. Two infrared cameras were mounted in the experimental room. During the experiment, a trained personnel would stay in the monitoring room to monitor the participant. Both rooms were air-conditioned and the temperature was maintained between 24 to 26 degrees centigrade.

Questionnaires

This study used various questionnaires to assess parameters related to the participants’ subjective sleep quality. All of these were designed based on Practice of Sleep Medicine 26 , which is the official guideline of TSSM. A pre-session questionnaire (questionnaire A) was administrated before the sleep session started. It includes 11 questions about the participant’s daily activity, their psychological status and their intake of alcoholic/caffeine drink (Table S1 ). This questionnaire was used to ensure that the participant was in their usual state during monitored sleep sessions. A post-session questionnaire (questionnaire B) was administrated right after the sleep session ended. It includes 12 multiple choices questions about the participant’s sleep experience (Table S2 ). Like the sleep diary, questionnaire B would derive 4 sleep quality indexes that reflect the participant’s subjective sleep quality. Various Stanford Sleepiness (SSS) questionnaires 27 were filled in the following day to evaluate daytime sleepiness of the participant on a scale of 1 to 7 (Table S3 ) (Higher means sleepier).

Experiment procedure

Each participant was recorded for two nights. One of the nights would be chosen as the stimulus night while the other night was used as control. The orders of control night and stimulus night among the participants were counterbalanced. Half of the participants would receive aroma stimuli at first night while the other half would receive the stimuli on second night. Before both stimulus and control night, the participants were told to do their usual activities and not to take a nap or any alcoholic/caffeine drink during the preceding day. The participants would arrive at the sleep lab at around 10:30 PM to perform an olfactory function check and fill out questionnaire A. They would then go to bed at 11:30 PM and be woken at 7:30 AM. When the participants woke up, they were asked if they noticed any smell during their sleep. They were then asked to fill out questionnaire B. During the ensuing day, the participants were asked to record a SSS questionnaire score every 2 h from 8:00 AM to 4:00 PM (Fig.  1 ).

Experimental flowchart.

During the stimulus night, essential oil of Lavandula angustifolia was repeatedly released starting from 1.5 h after bedtime to 1.5 h before the waking. This is done to prevent the participants from noticing the scent of essential oil. Each release was held for 1 min and then dropped for 4 min to avoid olfactory fatigue (Fig.  1 ). During the control night, the essential oil dispenser was configured as in stimulus night to avoid alerting the participant. Instead of essential oil, water vapor was released in control night.

Signal recording and processing

EEG, EOG and EMG signals were recorded using the CURRY Scan NuAmps Express system (Compumedics Neuroscan, Charlotte, NC, USA). Electrodes were secured for recording 20 channels of EEG with the 10/20 International Placement System. All EEG signals were re-referenced to the opposite lateral mastoids. Two EOG channels (LEOG, REOG) and one chin EMG were recorded simultaneously to help classifying sleep stage. All signals were recorded at a sample rate of 500 Hz.

Signals from 8 EEG channels (F3, F4, C3, C4, P3, P4, O1, and O2), all EOG channels and the chin EMG channel were used for sleep stage classifying. The signals were filtered with a band-pass filter at 10–70 Hz and then resampled to 128 Hz. All signals were then divided into 30-s epochs. Each epoch was scored and labeled visually based on the manual scoring rules of AASM 20 by an experienced sleep technologist. All signal processing and analysis were performed using MATLAB (2019a., The MathWorks, Natick, MA, USA).

To observe EEG spectral changes induced by lavender stimuli, EEG epochs from control night and stimuli night during the lavender aroma releases were selected to generate power spectrum (Fig.  2 ). Raw signals from Fz, Cz, and Oz channels were filtered with a band-pass filter at 0.3–35 Hz and a 60 Hz notch filter. They were then resampled from 500 to 250 Hz to reduce computational complexity. We used short-time Fourier transform (STFT) with 2-s Hamming window overlapped with a 1-s window to estimate their power spectrum density (PSD) of the epochs. For each EEG channel, the first two N1 epochs after sleep onset were used as the baseline epochs, as their variations were smaller than that of the first PSG epoch (usually wake stage). The average PSD of the two epochs was used as the baseline PSD for each channel. PSDs from various EEG epochs were grouped by their sleep stages label and then averaged. Power spectra of. Power spectra of T3 and T4 were derived in the same manner to observe olfactory-related activities in temporal lobe.

EEG power spectrum density analysis flowchart.

Statistical analysis

Subjective (questionnaires) and objective (PSG reports) sleep quality comparisons were done by using Wilcoxon signed-rank test due to small sample size (nine participants) and the results don’t follow normal distribution. As for EEG STFT PSD analysis, the Student t-test is used because the data amount is large enough.

Effect on subjective sleep quality

When being asked, none of the nine participants reported noticing scent of lavender during their sleep session in either stimulus night or control night. Participants showed significant differences in subjective sleep quality scores between post-session questionnaires from the stimulus nights and those from control nights (Fig.  3 A). Though ratings of sleep depth and sleep duration were roughly the same between stimulus and control nights (sleep depth: 5.6 ± 0.8 vs. 4.3 ± 1.1; p > 0.5; sleep duration: 4.6 ± 1.1 vs. 4.3 ± 0.8; p > 0.5), the rating of sleep disturbance in stimuli night was lower than in control night (2.8 ± 1.1 vs. 4.6 ± 1.1; p = 0.01). On the other hand, ratings of sleep wellness from stimulus night were higher than control nights (5.4 ± 1.0 vs. 4.2 ± 1.0; p = 0.01). The SSS questionnaire ratings after the stimulus nights were significantly lower than those following the control nights (Fig.  3 B). These results show that lavender aroma could improve subjective sleep quality.

Lavender aroma stimuli improved subjective sleep quality. ( A ) Sleep indexes from questionnaire B. Sleep Disturbance was decreased while sleep wellness was increased in stimuli night. ( B ) Daytime SSS questionnaire ratings. SSS rating after stimuli night was higher than that of control night from 10:00 AM to 4:00 PM.

Lavender aroma induced EEG changes in different sleep stages

Since lavender aroma improved subjective sleep quality, we proceeded to inspect its effect on brain wave activity by analyzing the EEG power spectra changes upon release of lavender aroma. The analysis showed that lavender aroma affected multiple brain regions across different sleep stages (Fig.  4 ). In wake stage, alpha and beta power were significantly decreased in Cz, Fz, Oz, T3, and T4. Additionally, the Fz channel showed increased slow delta activity towards the end of wake stage. The decreased alpha activity across multiple brain regions, especially in the motor cortex and frontal lobes, implies that there were less sleep interruptions and limb movements during the stimulus night.

EEG spectrum during the release of lavender oil. ( A ) Cz channel, ( B ) Fz channel, ( C ) Oz channel, ( D ) T3 channel, ( E ) T4 channel.

In N3 stage and REM stage, T3 and T4 (representing left and right temporal lobe respectively) showed a slightly different pattern. While T3 showed increased beta power in N3, T4 showed decreased beta power. All the five channels, including T3 and T4, showed significant decreases in alpha power and increases in delta power. This result indicates that sleep during stimulus nights was deeper and more stable. Similar changes could also be seen during REM stage as well.

Lavender aroma induced changes in sleep stages

We proceeded to examine the distribution of sleep stages among our participants. The sleep EEG recordings showed that there was no difference in total time in bed (TIB) (455 ± 66 min vs. 453 ± 53 min; p > 0.05) between stimulus and control conditions. There was no difference in sleep efficiency (SE) (91.1 ± 5.9% vs. 91.8 ± 4.8%; p > 0.05), and wake after sleep‐onset (WASO) (8.9 ± 5.9% vs. 8.3 ± 4.8%; p > 0.05) either. These suggest that the participants slept for roughly the same amount of time in both control and stimulus nights (Table 1 ). While the time percentages of N1, N2 and REM relative to TIB showed no difference between conditions, time percentage of N3 for the stimulus night was significantly higher than that for control night (21.9 ± 5.6% vs. 19.4 ± 5%; p = 0.01) (Fig.  5 A). This suggests that although participants slept for roughly the same time with or without lavender aroma, they spent more time in N3 when the lavender stimulus was present. Similar phenomenon can be seen when we replaced TIB with total sleep time (TST). Time percentage of N3 relative to TST is higher for the stimulus night than that for the control night (23.9 ± 5.8% vs. 21.1 ± 4.9%; p = 0.01). In contrast, percentage of N2 was lower for the stimulus night than for the control night (46.6 ± 3.3% vs. 50.2 ± 5.7%; p = 0.05) (Fig.  5 B). When examining the participants’ hypnograms, we found that the N3 stages were longer and more frequent upon lavender releases (Fig.  6 ). These results confirmed that sleep in stimulus nights were indeed deeper and more stable. Overall, these results suggest that lavender aroma can reduce alpha power and promote delta power in the sleeping brain, leading to deeper sleep and improved sleep quality.

Lavender aroma promotes deeper sleep stages. ( A ) Sleep stages percentage in TIB. Percentage of N3 stage was increased in stimuli night. ( B ) Sleep stages percentage in TST. Percentage of N3 stage was increased while that of N2 was decreased in stimuli night.

Hypnogram of one of the participants (S1) drawn by sleep technician. N3 showed the same pattern in stimuli night and control night before stimuli onset (green arrow). Upon stimuli onset, N3 became longer and more frequent (orange arrow).

There have been multiple claims about essential oil’s positive effects on sleep quality over the last two decades 11 , 12 , 13 , 14 , 15 . However, the mechanisms of aroma remain a debated topic. The nature of aromatherapy has made it hard to exclude psychological factors from experiment designs. In this study, we designed a single-blinded experiment to overcame the limitation of aroma study. By randomly selecting stimulus nights and only releasing lavender aroma when the participants were asleep, we were able to keep the participants blinded and reduce influence of their psychological expediencies to the minimum. All participants experienced less disturbance and better sleep quality during stimuli nights. Their EEG recordings further confirmed the benefit of lavender oil as they showed increased delta activity in deep sleep and reduced alpha/beta activity during wake stages. Our study not only suggests that lavender aroma may promote sleep quality by influencing sleep brain activity directly, but also demonstrated that blinded study of aromatherapy is achievable.

In their subjective questionnaires, the participants reported decreased sleep disturbance and increased sleep wellness during stimulus nights. Although total wake stage duration was not reduced during stimulus nights, EEG power analysis shows that wake stage alpha and beta power were reduced in frontal lobe and motor cortex. Previous study done by Halász et al. 28 suggested that there are different types of awakening in mammal sleep. Schwabedal et al.’s study 22 found that short WASOs have much less alpha activity than longer (> 5 min), more perceivable WASOs. They went on to propose that the long and short WASOs might be fundamentally different. Although our studies did not observe any difference in WASO duration between control and stimulus night, our participants did report reduced sleep disturbances in stimulus nights. It is possible that by reducing alpha activity, lavender aroma was able to make longer WASOs more like shorter WASOs and make them less perceivable for the participants, though more studies need to be done to verify this phenomenon.

During the experiment, the participants showed no significant differences in SE between stimulus and control nights. This suggests that lavender aroma did not affect the sleep/wake ratio in healthy young adults. On the other hand, the participants showed increased SWS and reduced N2 in stimulus night. The increase of SWS is synchronous with lavender releases as shown in Fig.  6 , suggesting that these increases are caused by lavender oil stimuli. SWS is not only important to daytime vigor but also overall health of brain as well. Recent study by Fultz et al. 23 revealed that occurrence of SWS is followed by large volumes of fluid exchange in human brain. This suggests that SWS is not just vital for daytime vigor and performance, but also removal of harmful materials. Several neurodegenerative disorders like Alzheimer’s disease (AD) and Parkinson’s disease (PD) are related to accumulation of toxic protein debris 29 , 30 . Study by Varga et al. 31 has shown that elderly people with longer SWS time have lower concentration of AD-inducing protein debris in CSF when they woke up. Our finding suggests that lavender aroma may be used to increase SWS in sleep and help prevent neurodegenerative diseases even when total sleep time is limited. As sleep time is often limited due to the work constraints in modern society, sleep-time lavender aroma may provide a cheap, safe way to improve sleep quality and prevent diseases like AD with minimal alteration of personal schedules and/or sleep/wake cycle.

We observed that temporal activity is significantly increased upon lavender aroma release. This confirms previous studies suggesting that the human brain can process olfactory stimuli during sleep 32 , 33 . The increased activities in the temporal lobes were simultaneous with increased delta power and decreased alpha power in other brain regions. This suggests the increased sleep quality is directly related to aroma stimuli. Perl et al. 34 found that lavender stimuli increase delta activity in NREM sleep. Their results showed that odor release duration is positively related with the time span of increased delta activity, which is consistent with our study. On the other hand, studies on wake time EEG reported that lavender aroma increases alpha and theta wave activity instead of delta activity 24 , 25 , which are different from our and Perl et al.’s results. This implies that sleeping brain and wake brain react differently to lavender stimuli. More studies are required to clarify how lavender aroma affects brain activity. It is also worth exploring aroma of other essential oils or herbs that are suspected to improve sleep quality, such as chamomile 35 .

This study observed that lavender aroma promotes deep sleep when inhaled asleep. In the stimulus night, SWS percentage was increased and N2 percentage was decreased in relation to TST. It is not clear how lavender aroma achieve such effect, either by pushing brain in N2 stage into SWS, or by keeping brain in SWS from bouncing back to light sleep. More studies need to be done to determine which one is the dominant mechanism. In both cases, lavender aroma could benefit from automated, real-time sleep stage classifying. By releasing the aroma at the right stage through brain-computer interface (BCI), we can maximize the effect of aroma appliance. Curiously, previous study by Rasch et al. showed that odor cue during SWS can promote consolidation of memory related to the cue 32 . This means that a BCI-controlled aroma releasing system may not only improve sleep quality and toxic material removal but also aid in daytime learning. Automated sleep stage classifying is a hot topic in recent years 36 , 37 , 38 , though most proposed methods conduct the classifying post hoc instead of in real-time. We’re currently improving a time-independent classifying algorithm we proposed earlier 39 . The algorithm only requires two forehead EEG channels for feature extraction, which makes it particularly suitable for sleep BCI application. We’re looking forward to exploring the potential of BCI-controlled SWS enhancing system.

Linalool, a compound that can stimulate parasympathetic neurons 35 , has long been suspected to be the key to lavender’s effect in reducing anxiety and improving sleep quality. Oral extract of Lavandula angustifolia containing linalool has been reported to improve sleep quality in patients with anxiety disorder 40 . However, recent study done by Seifritz et al. 41 suggested that the extract has a long (about 2 weeks) delay in its effect on sleep quality and does not improve sleep quality in subjects with low anxiety. In this study, we demonstrated that lavender aroma stimulus changes the brain activity and improve sleep quality very quickly. Our participants reported experiencing better sleep quality and more daytime vigor after just one night of exposure. Our findings hint that inhaling essential oil may influence brain activity through different mechanism than that of oral consumption of lavender or lavender extract. A combination of oral extract intake and sleep-time aromatherapy may achieve greater effects than applying these two methods separately. As insomnia becomes more prevalent in modern society, lavender may provide a safe, effective way in combating sleep-related problems.

Despite showing promising result, this study has some major limitations. The first limitation is that the sample size was rather small. The small sample size may not be strong enough to justify a new aroma-based treatment for sleep deprivation or other sleep disorder. The second limitation is that our study only included young adults. The aim of this study is to explore the effect of aroma oil on human sleep pattern and EEG. More studies with bigger and more diverse sample would be needed to determine the underlying mechanism and clinical potential of essential oil aroma on sleep.

By utilizing a single-blinded design, our study was able to demonstrate that essential oil aroma may have positive effects on objective and subjective sleep quality in healthy young adults. None of our 9 participants reported smelling lavender during stimulus night, while experience more vigor in the following day. EEG power analysis showed that our participants showed decreased alpha activity and increased delta activity upon aroma release. These results suggest that the improved sleep quality is directly linked to aroma. Furthermore, our study found that SWS was increased in stimulus night. This study could serve as a pilot for future study on aroma and cognitive function and improve application of aroma in the future.

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Acknowledgements

This study was founded by Center for Intelligent Drug Systems and Smart Bio-devices (IDS2B) from The Featured Areas Research Center Program within the framework of the Higher Education Sprout Project, Ministry of Education (MOE), Taiwan.

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Li-Wei Ko, Cheng-Hua Su & Meng-Hsun Yang

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Shen-Yi Liu

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M.H.Y. and L.W.K. approached and designed this study. M.H.Y. and C.H.S. conducted data curation and statistics analysis. M.H.Y., L.W.K., C.H.S., T.P.S. and S.Y.L. provided concept of the paper and interpreted the data being published. C.H.S. and M.H.Y. wrote the initial manuscript. L.W.K. and C.H.S. reviewed and revised the manuscript.

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Ko, LW., Su, CH., Yang, MH. et al. A pilot study on essential oil aroma stimulation for enhancing slow-wave EEG in sleeping brain. Sci Rep 11 , 1078 (2021). https://doi.org/10.1038/s41598-020-80171-x

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The Science of Essential Oils: Does Using Scents Make Sense?

More and more Americans may have heard some buzz about essential oils, and may be experimenting with them in hopes of improving their moods or feeling better. These fragrant oils, such as lavender, peppermint, eucalyptus, orange and tea tree, are extracted from a plant's leaves, flowers, roots, barks, seeds or peels.

People may turn to essential oils as part of aromatherapy, an alternative-medicine approach in which these highly concentrated, aromatic plant oils are used in small amounts in hopes of improving someone's physical or emotional health. The oils are sold online and in natural food stores.

But although many essential oils have pleasant smells and some of their active ingredients are purported to have health benefits, there is limited scientific evidence that they actually improve people's health or mood. And even small vials of these concentrated oils can be pricey.

Essential oils are mixtures, sometimes containing almost 300 substances, said Gerhard Buchbauer, a professor of pharmaceutical chemistry at the University of Vienna in Austria, who has researched and written about the chemical compounds used in aromatherapy. The oils contain both simple and complex chemicals, he said.

Pure essential oils are free of aromatic compounds called polycyclic aromatic hydrocarbons (PAHs), which may be linked with cancer, but they do contain volatile organic compounds (VOCs) — otherwise, they could not be smelled, Buchbauer said.

Using the active compounds in essential oils in low concentrations and inhaling the vapors of these oils are normally safe for most people, Buchbauer said. Safety testing of essential oils have shown they have few negative side effects, when used as directed. [ 5 Wacky Things That Are Good for Your Health ]

However, research suggests that because some of the oils mimic the female hormone estrogen, they may have unwanted effects on males. Lavender oil and tea tree oil may cause enlarged breast tissue in prepubertal boys, according to a 2007 study in the New England Journal of Medicine.

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How essential oils are used   

Aromatherapists recommend the oils be directly inhaled from a bottle, cloth or palm of the hand, or massaged into the skin after being diluted in a carrier oil, such as olive oil or almond oil.

When inhaled, "the absorption of essential oils by the nose is as fast as an intravenous injection," Buchbauer said.Essential oils are sometimes called volatile oils, meaning they evaporate quickly when exposed to the air, which releases their scents.

In comparison, the absorption of essential oils through the skin is slower, because some of their chemical compounds need to pass through the fat layers under the skin and may even get stored there, Buchbauer said.

He stressed that because of their potency, it's important to use only a few drops of a diluted form of essential oils when applying them to the skin. Unless they are diluted, essential oils can irritate the skin.

Some consumers add essential oils to their baths, or use them as home remedies, such as inhaling eucalyptus vapors to relieve congestion.Others may place the oils in a diffuser to scent the air — peppermint is promoted for stimulating alertness, and lavender is often listed as a way to promote calmness, although there are no rigorous studies to support such claims .

Do-it-yourselfers may add drops of essential oils when making natural beauty products to give them fragrance, or use them in green cleaning products because of their disinfectant or cleansing properties. 

Limited evidence

Smell plays a big role in how essential oils may affect the body: When breathed in, these plant oils stimulate smell receptors in the nose that send chemical messages through nerves to the brain's limbic system, which affects moods and emotions, and may have some physiological effects on the body, according to the National Institutes of Health (NIH). (When used on the skin, the oils are absorbed into the bloodstream.)

Some oils may cause skin irritation or allergic reactions, which is why people should test their sensitivity to an oil on a small patch of skin, before they begin to use an oil more broadly, said Dr. Wolfgang Steflitsch, a chest physician at Otto Wagner Hospital in Vienna, and vice president of the Austrian Association of Aromatherapy and Aroma Care. He also said that certain citrus oils when applied to the skin can increase sun sensitivity, and that some substances in essential oils may be risky for pregnant women.

Although Americans may think of aromatherapy as part of a spa or beauty treatment, medical aromatherapy is popular in Europe, where some physicians may prescribe and use the oils therapeutically as part of complementary medical care. [ 9 Healthy Habits You Can Do in 1 Minute (Or Less) ]

About 100 different essential oils are used for medical aromatherapy in Austria and other European countries, Steflitsch told Live Science.

One example of oil that shows some evidence of effectiveness is tea tree oil, which may be an effective treatment for acne , according to the NIH. In one clinical trial, researchers compared gel containing tea tree oil to a benzoyl peroxide product, and found that the benzoyl peroxide worked slightly better but that the tea tree oil had fewer side effects, according to the NIH.

A few preliminary studies have suggested that peppermint oil may help with irritable bowel syndrome. Although the oil is touted for working as a decongestant and reliving headaches and muscle pain, "there is no clear-cut evidence to support the use of peppermint oil for other health conditions," the NIH says on its website. Capsules of peppermint oil may cause heartburn.

Lavender oil is claimed to have a slew of a health benefits, with aromatherapy practitioners using it for anxiety, restlessness, insomnia, depression , headache, upset stomach and hair loss. Some small studies on using lavender for anxiety have yielded mixed results, and some studies suggest the oil may work in combination with other oils to fight a hair-loss condition called alopecia areata, according to the NIH. However, "there is little scientific evidence of lavender's effectiveness for most health uses," the NIH says.

Steflitsch said that aromatherapy is an offshoot of herbal medicine , and European patients and physicians have traditionally been more open to using plant-based therapies as part of their medical treatment compared with the United States, which has a different legal and regulatory climate.

Steflitsch said there is some high-quality evidence that essential oils are effective in treating viral, bacterial, fungal and parasitic infections, and in providing relief from sleep difficulties and pain. The oils may also improve moods, such as anxiety, depression, and reduce stress.

But American physicians typically look to research from clinical trials to determine the effectiveness of medical treatments, and many of the existing studies on essential oils are small. They do not meet this "gold standard" criteria.

Follow Live Science @livescience , Facebook   & Google+ . Originally published on Live Science .

Cari Nierenberg has been writing about health and wellness topics for online news outlets and print publications for more than two decades. Her work has been published by Live Science, The Washington Post, WebMD, Scientific American, among others. She has a Bachelor of Science degree in nutrition from Cornell University and a Master of Science degree in Nutrition and Communication from Boston University.

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Although essential oils have been used therapeutically for centuries, there is little published research on many of them. However, this is beginning to change as more scientific studies on essential oils are conducted around the world.

Clinical studies are currently underway in Europe, Australia, Japan, India, the United States, and Canada. Many of these studies describe the remarkable healing properties of various oils.

Who is doing the research?

Although much of this research is proprietary and not generally available to consumers, some of it has made its way into cosmetic and plant product journals. These journals are important sources of information as we accumulate a growing body of knowledge on essential oils.

Most of the studies that have been published in the English language scientific literature have been conducted in laboratories and they have not been tested on humans, but this is changing.

What are some issues in conducting research on essential oils?

Essential oils are not standardized..

The chemistry of essential oils is influenced by the local geography and weather conditions, as well as the season and time of day when the plants are harvested, how they are processed, and how they are packaged and stored. Each plant is unique in its chemistry so essential oils are never exactly the same-this is different from pharmaceutical drugs that are synthetically reproduced to be identical every time. Essential oils can be altered to achieve standardization (for example, a certain chemical that was found to be at a lower concentration in the whole oil in a particular year can be added to make it the same percentage as last year's batch). The problem with standardized essential oils is that they are no longer natural, genuine, and authentic. This variability in essential oils by time, place and conditions is a big challenge to conducting valid research. Currently the International Standards Organization sets standards for each essential oil that include a range of acceptable concentrations for its major chemical constituents.

It is difficult to conduct blinded studies with aromatic substances.

Typical research studies involve testing two groups-one group gets an experimental substance and another group gets a placebo substance (this group is referred to as the "control" group). When using aromatic substances, it is very difficult to conduct a blinded study. Some researchers have used masks or other barriers to blind participants. Other researchers have used alternate scents assumed to have no therapeutic properties as controls. These approaches are problematic, however, because people associate smells with past experiences. Thus, it is difficult to account for individual variation in how essential oils affect people.

It is difficult to get approval and funding for research on essential oils.

Essential oils have been used on humans for thousands of years. As a result, they don't fit into the conventional clinical science approach of testing a substance in the lab first, then on animals, and then on humans. As a result, if a researcher proposes to test an essential oil with humans first, they may be turned down. This is because research review boards tend to approve research studies that follow the more usual scientific research path. Many conventional drug studies are funded by the pharmaceutical industry. There is little motivation for these companies to fund research on natural plant substances because they cannot easily be patented, limiting the potential for profit. Thus, finding funding for essential oils studies can be challenging.

It is difficult to tell what caused the outcome.

In conventional research studies, it is important to be able to determine exactly what caused the outcome. In essential oil therapy, the oils are sometimes applied with massage, which makes it difficult to tell whether or not the outcome was due to the essential oil alone, or the massage, or the combination. Also, essential oils are composed of hundreds of chemical constituents, and it is hard to determine which ones may have produced the desired effect.

What does the research say?

Research studies on essential oils show positive effects for a variety of health concerns including infections, pain, anxiety, depression, tumors, premenstrual syndrome, nausea, and many others. The resources on this page are meant to highlight a few examples.

Aromatherapy online course

Want to learn more? The University of Minnesota offers an online course in Fundamentals of Aromatherapy .

Alexandrovich, I., Rakovitskaya, O., Kolmo, E., Sidorova, T., Shushunov, S. (2003). The effect of fennel (Foeniculum Volgare) seed oil emulsion in infantile colic: a randomized, placebo-controlled study. Alternative Therapies in Health and Medicine, 9(4), 58-61.

Al-Hader, A.A., Hasan, Z.A., Aqel, M.B. (1994). Hyperglycemic and insulin release inhibitory effects of rosmarinus officinalis. Journal of Ethnopharmacology, 43 , 217,22.

Al-Shuneigat, J., Cox, S. D., & Markham, J. L. (2005). Effects of a topical essential oil-containing formulation on biofilm-forming coagulase-negative staphylococci. Letters in Applied Microbiology , 41 (1), 52-55.

Anderson, L., Gross, J. (2004). Aromatherapy with peppermint, isopropyl alcohol, or placebo is equally effective in relieving postoperative nausea. Journal of Peri-Anesthesia Nursing , 19 (1), 29-35.

Bagg, J., Jackson, M. S., Petrina Sweeney, M., Ramage, G., & Davies, A. N. (2006). Susceptibility to melaleuca alternifolia (tea tree) oil of yeasts isolated from the mouths of patients with advanced cancer. Oral Oncology, 42 (5), 487-492.

Ballard, C.G., O'Brien, J.T., Reichelt, K., Perry, E.K. (2002). Aromatherapy as a safe and effective treatment for the management of agitation in severe dementia: the results of a double-blind, placebo-controlled trial with Melissa. Journal of Clinical Psychiatry, 63 , 553-8.

Barker, S & Altman P. (2010). A randomized, assessor blind, parallel group comparative efficacy trial of three products for the treatment of head lice in children - melaleuca oil and lavender oil, pyrethrins and piperonyl butoxide, and a "suffocation" product. BMC Dermatology, 10 , 6.

Bassett, I. B., Pannowitz, D. L., & Barnetson, R. S. (1990). A comparative study of tea-tree oil versus benzoylperoxide in the treatment of acne. Med J Aust, 153 (8), 455-458.

Benencia, F. (1999). Antiviral activity of sandalwood oil against Herpes simplex viruses-1 and -2. Phytomedicine, 6 (2), 119-23.

Bernardes W, Lucarini R, Tozatti M, Flauzino L, Souza M, Turatti I, Andrade e Silva M, martins C, da Silva Filho A & Cunha W. (2010). Antibacterial activity of the essential oil from Rosmarinus officinalis and its major components against oral pathogens. Journal of Biosciences; 65 (9-10):588-93.

Bouhdid, S, Abrini, J, Zhiri, A, Espuny, M & Manresa, A. (2009). Investigation of functional and morphological changes in Pseudomonas aeruginosa and Staphylococcus aureus cells induced by Origanum compactum essential oil. Journal of Applied Microbiology, 106 (5), 1558-1568.

Brady, A., Loughlin, R., Gilpin, D., Kearney, P., & Tunney, M. (2006). In vitro activity of tea-tree oil against clinical skin isolates of meticillin-resistant and -sensitive staphylococcus aureus and coagulase-negative staphylococci growing planktonically and as biofilms. Journal of Medical Microbiology, 55 (Pt 10), 1375-1380.

Brandao, F. M. (1986). Occupational allergy to lavender oil. Contact Dermatitis , 249-50.

Buckle, J. (2007). Literature review: should nursing take aromatherapy more seriously? British Journal of Nursing, 16 (2), 116-120.

Burns, E., Blamey, C., Ersser, S. J., Barnetson, L., & Lloyd, A. (2000). An investigation into the use of aromatherapy in intrapartum midwifery Practice. The Journal of Alternative and Complementary Medicine, 6 (2), 141-7.

Burns, E., Zobbi, V., Panzeri, D., Oskrochi, R., Regalia, A. (2007). Aromatherapy in childbirth: a pilot randomized controlled trial. BJOG: An International Journal of Obstetrics & Gynaecology, 114 (7), 838-44.

Burt, S. A. (2003). Antibacterial activity of selected plant essential oils against Escherichia coli O157:H7. Letters in Applied Microbiology 36, 162-7.

Caelli, M., Porteous, J., Carlson, C. F., Heller, R., & Riley, T. V. (2001). Tea tree oil as an alternative topical decolonization agent for methicillin-resistant Staphylococcus Aureus. The International Journal of Aromatherapy, 11 (2). [Originally published in The Journal of Hospital Infection (2000), 46, 236-237.]

Canyon, D & Speare, R. (2007). A comparison of botanical and synthetic substances commonly used to prevent health lice (Pediculus humanus var. capitis) infestation. International Journal of Dermatology, 46 (4), 422-426.

Cappello, G, Spezzaferro, M, Grossi, L, et al. (2007). Peppermint oil (Mintoil) in the treatment of irritable bowel syndrome: A prospective double blind placebo-controlled randomized trial. Digestive & Liver Disease, 39 (6), 530-536.

Carson, C. F., Hammer, K. A., & Riley, T. V. (2006). Melaleuca alternifolia (tea tree) oil: A review of antimicrobial and other medicinal properties. Clinical Microbiology Reviews, 19 (1), 50-62.

Chang, SY. (2008). Effects of aroma hand massage on pain, state anxiety and depression in hospice patients with terminal cancer. Daehan Ganho Haghoeji, 38 (4), 493-502.

Chung, M, Cho, S, Bhuiyan, M, Kim, K & Lee, S. (2010). Anti-diabetic effects of lemon balm (Melissa officinalis) essential oil on glucose- and lipid-regulating enzymes in type 2 diabetic mice. British J of Nutrition, 104 (2), 180-188.

Cooke, B., Ernst, E. (2000). Review: aromatherapy massage is associated with small, transient reductions in anxiety. British Journal of General Practice, 50 , 493-6.

Davies, SJ, Harding, LM & Baranowski, AP. (2002). A novel treatment of postherpetic neuralgia using peppermint oil. Clinical Journal of Pain, 18 (3), 200-2.

De Groot, A.C., & Weyland, W. (1992). Systemic contact dermatitis from tea tree oil. Contact Dermatitis, 27 , 279-80.

Dryden, M., Dailly, S., Crouch, M. (2004). A randomized, controlled trial of tea tree topical preparations versus a standard topical regimen for the clearance of MRSA colonization. Journal of Hospital Infec, 56 (4), 283-6.

Dwivedi, C. & Zhang, Y. (1999). Sandalwood oil prevents skin tumour development in CD1 mice. European Journal of Cancer Prevention, 8 , 449-55.

Edris, A. (2007). Pharmaceutical and therapeutic potentials of essential oils and their individual volatile constituents: A review. Phytotherapy Research, 21 , 308-323.

Enshaieh, S., Jooya, A., Siadat, A. H., & Iraji, F. (2007). The efficacy of 5% topical tea tree oil gel in mild to moderate acne vulgaris: A randomized, double-blind placebo-controlled study. Indian Journal of Dermatology, Venereology & Leprology, 73 (1), 22-25.

Furneri, P. M., Paolino, D., Saija, A., Marino, A., & Bisignano, G. (2006). In vitro antimycoplasmal activity of melaleuca alternifolia essential oil. Journal of Antimicrobial Chemotherapy, 58 (3), 706-707.

Gao, Y. Y., Di Pascuale, M. A., Li, W., Baradaran-Rafii, A., Elizondo, A., Kuo, C. L., et al. (2005). In vitro and in vivo killing of ocular demodex by tea tree oil. British Journal of Ophthalmology, 89 (11), 1468-1473.

Garozzo A, Timpanarao R, Stivala A, Bisignano G & Castro A. (2010) Activity of Melaleuca alternifolia (tea tree) oil on influenza virus A/PR/8: Study on the mechanism of action. Antiviral Research, 89 (1), 83-8.

Gedney, J., Glover, T., Fillingim, R. (2004). Sensory and affective pain discrimination after inhalation of essential oils. Psychosomatic Medicine, 66 (4), 599-606.

Greenway, f, Frome & Engels, T. (2003). Temporary relief of postherpetic neuralgia pain with topical geranium oil. American J of Medicine, 115 , 586-587.

Gustafson, J. E., Chew, S., Markham, J., Bell, H.C., Wyllie, S. G., & Warmington, J. R. (1988). Effects of tea tree oil on Escherichia coli. Letters in Applied Microbiology, 26 , 194-8.

Hadfield, N. (2001). The role of aromatherapy massage in reducing anxiety in patients with malignant brain tumors. International Journal of Palliative Nursing, 7 (6), 279-285.

Hajhashemi, V., Ghannadi, A., & Sharif, B. (2003). Anti-inflammatory and analgesic properties of the leaf extracts and essential oil of lavandula angustifolia mill. Journal of Ethnopharmacology, 89 (1), 67-71.

Halm, M. (2008). Essential oils for management of symptoms in critically ill patients. American Journal of Critical Care, 17 (2), 160-163.

Hammer, K. A., & Riley, T. V. (1998). In-vitro activity of essential oils, in particular Melaleuca alternifolia (tea tree) oil and tea tree oil products, against Candida spp. J ournal of Antimicrobial Chemotherapy, 42, 591-5.

Hammer, K. A., Carson, C. F., & Riley, T. V. (2004). Antifungal effects of melaleuca alternifolia (tea tree) oil and its components on candida albicans, candida glabrata and saccharomyces cerevisiae. Journal of Antimicrobial Chemotherapy, 53 (6), 1081-1085.

Hammer, K. A., Carson, C. F., Riley, T. V., & Nielsen, J. B. (2006). A review of the toxicity of Melaleuca alternifolia (tea tree) oil. Food & Chemical Toxicology, 44 (5), 616-625.

Han, S., Hur M., Buckle, J., Choi, J., Lee, M. (2006). Effect of aromatherapy on symptoms of dysmenorrheal in college students: A randomized placebo-controlled clinical trial. The Journal of Alternative and Complentary Medicine, 12 (6), 535-41.

Hansen, T., Hansen, B., Ringdal, G. (2006). Does aromatherapy massage reduce job-related stress? Results from a randomized, controlled trial. International Journal of Aromatherapy, 16 (2), 89-94.

Hayashi, K., & Hayashi, T. (1994). Virucidal effects of the steam distilate from Houttuynia cordata and its components on HSV-1, influenza virus, and HIV. Planta Medica, 61 , 237-41.

Haze, S, Sakai, K & Gozu, Y. (2002). Effects of fragrance inhalation on sympathetic activity in normal adults. Japanese Journal of Pharmacology, 90, 247-253.

Henley, D., Lipson, N., Korach, K., Bloch, C. (2007). Prepubertal gynecomastia linked to lavender and tea tree oils. The New England Journal of Medicine, 356 (5), 479-485.

Inouye, S., Yamaguchi, H. (2001). Antibacterial activity of essential oils and their major constituents against respiratory tract pathogens by gaseous contact. Journal of Antimicrobial Chemotherapy, 47 , 565-73.

Itai, T., Amayasu, H., Kuribayashi, M., Kawamura, N., Okada, M., Momose, A., Tateyama, T., Narumi, K., Waka, Kaneko, U.S. (2000). Psychological effects of aromatherapy on chronic hemodialysis patients. Psychiatry and Clinical Neurosciences, 54, 393-7.

Jandourek, A. & Vazquez, J. (1998). Efficacy of melaleuca oral solution for the treatment of fluconazole refractory oral candidiasis in AIDS patients. AIDS, 12, 1033-7.

Kane, FM, Brodie, EE, Couli, A, et al. (2004). The analgesic effect of odour and music upon dressing change. British Journal of Nursing, 13 (19), S4-12.

Kejova K, Jorova D, Bendova H, Gajdos P & Kolarova H. (2010). Phototoxicity of essential oils intended for cosmetic use. Toxicology in Vitro, 24 (8), 2084-9.

Khan, M, Zahin & Hassan, S. (2009). Inhibition of quorum sensing regulated bacterial functions by plant essential oils with special reference to clove oil. Letters in Applied Microbiology, 49 , 354-360.

Kim, J. et al. (2006). Evaluation of aromatherapy in treating post-operative pain: pilot study. Pain Practice, 6 (4), 273-277.

Lehrner, J., Marwinski, G., Lehr, S., Johren, P., & Deecke, L. (2005). Ambient odors of orange and lavender reduce anxiety and improve mood in a dental office. Physiology & Behavior, 86 (1-2), 92-95.

Lemon, K. (2004). An assessment of treating depression and anxiety with aromatherapy. The International Journal of Aromatherapy, 14 , 63-69.

Lucks, B.C., Sorensen, J., Veal, L. (2002). Vitex agnus-castus essential oil and menopausal balance: a self-care survey. Complementary Therapies in Nursing and Midwifery, 8 , 148-54.

Messager, S., Hammer, K. A., Carson, C. F., & Riley, T. V. (2005). Assessment of the antibacterial activity of tea tree oil using the european EN 1276 and EN 12054 standard suspension tests. Journal of Hospital Infection, 59 (2), 113-125.

Millar, B & Moore, J. (2008). Successful topical treatment of hand warts in a paediatric patient with tea tree oil (Melaleuca alternifolia). Complementary Therapies in Clinical Practice, 14 (4), 225-27.

Nguyen, Q., Paton C. (2008). The use of aromatherapy to treat behavioral problems in dementia. International Journal of Geriatric Psychiatry, 23 , 337-346.

Oyedele, A. O., Gbolade, A. A., Sosan, M.B., Adewoyin, F. B., Soyelu, O.L., & Orafidiya, O. O. (2002). Formulation of an effective mosquito-repellent topical product from Lemongrass oil. Phytomedicine, 9, 259-62.

Price, S. & Price, L. (2007). Aromatherapy for health professionals, 3rd Ed . Philadelphia: Churchill Livingstone Elsevier.

Rose, J. E. & Behm, F. M. (1994). Inhalation of vapor from black pepper extract reduced smoking withdrawal symptoms. Drug and Alcohol Dependence, 34 , 225-9.

Saeki, Y. (2000). The effect of foot bath with or without the essential oil of lavender on the autonomic nervous system: A randomized trial. Complementary Therapies in Medicine, 8, 2-7.

Sharma S, Araujo M, Wu M, Qaqush J & Charles C. (2010). Superiority of an essential oil mouthrinse when compared with a 0.05% cetylpyridinium chloride containing mouthrinse: A six-month study. International Dental Journal, 60 (3), 175-80.

Sherry, E., Warnke, P. H. (2001). Percutaneous treatment of chronic MRSA osteomyelitis with a novel plant-derived antiseptic. BMC Surgery, 1 (1).

Snow L, Hovanec L & Brandt J. (2004). A controlled trial of aromatherapy for agitation in nursing home patients with dementia. J Alternative & Complementary Medicine, 10 (3), 431-437.

Soukoulis, S., & Hirsch, R. (2004). The effects of a tea tree oil-containing gel on plaque and chronic gingivitis. Australian Dental Journal, 49 (2), 78-83.

Srivasta, K. C., Mustafa, T. (1992). Ginger (Zingiber officinale) in Rheumatism and Musculoskeletal Disorders. Medical Hypotheses, 39, 342-8.

Takarada, R. et al. (2004). A comparison of the antibacterial efficacies of essential oils against oral pathogens. Oral Microbiology and Immunology, 19 , 61-64.

Toloza A, Zygadlo J, Biurrun F, Rotman A & Picollo M. (2010). Bioactivity of Argentinean essential oils against permethrin-resistant head lice, Pediculus humanus capita. J of Insect Science, 10 , 185.

Torres Salazar A, Hoheisel J, Youns M & Wink M. (2011). Anti-inflammatory and anti-cancer activities of essential oils and their biological constituents. International J of Clinical Pharmacology & Therapeutics, 49 (1), 93-95.

Tyagi A & Malik A. (2010). Liquid and vapour-phase antifungal activities of selected essential oils against Candida albicans: Microscopic observations and chemical characterization of Cymbopogon citratus. BMC Complementary & Alternative Medicine, 10 , 65.

Van der Ploeg E, Eppingstall B & O'Connor D. (2010). The study protocol of a blinded randomized-controleed cross-over trial of lavender oil as a treatment of behavioural symptoms in dementia. BMC Geriatrics, 10 , 49.

Woelk, H & Schlafke, S. (2009). A multi-center, double-blind, randomizsed study of the lavender oil preparation Silexan in comparison to Lorazepam for generalized anxiety disorder. Phytomedicine, 17, 94-99.

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How to use essential oils, according to medical experts

You've likely seen — or smelled — essential oils before: Small bottles with potent scents, usually sold in stores surrounded by other "natural," "holistic" products.

Essential oils are fragrant plant extracts, made by steaming or pressing plants, according to Johns Hopkins Medicine . They're often used for aromatherapy, which a centuries-old practice of inhaling these oils or absorbing them through the skin with the goal of improving certain health ailments. There are dozens of types of essential oils, including lavender, tea tree, peppermint and lemon oils. Some celebrities, like Bella Hadid , swear by them.

If you're considering getting into the essential oil game, this is what medical experts want you to know first.

How to use essential oils

Essential oils are likely safe to inhale, University of Maryland School of Pharmacy assistant professor Lauren Hynicka, PharmD, BCPS, tells USA TODAY. You can add a few drops to a diffuser, cotton ball or nasal inhaler. If you're going to use them topically, make sure to dilute them in coconut or jojoba oil first.

And make sure you're investing in a high-quality essential oil — Johns Hopkins warns that some companies will dub their products "therapeutic-grade," but that's an unregulated marketing term, not a signifier that it's a product a medical expert would recommend.

What is the number one essential oil for anxiety?

Some research has shown that essential oils can offer some benefit for some health concerns. Lavender essential oil may be beneficial for anxiety , depression and sleep .

Experts caution that there's still a lot unknown about how essential oils work, because most of the studies conducted aren't the highest quality.

"Conducting high quality research with essential oils can be challenging," Hynicka says. She references double-blind studies, during which neither the study subject nor the researcher knows if a placebo or actual treatment is being used until the end to prevent bias.

But as Hynicka points out, it's tough to fake a placebo for essential oils: "Either you smell an essential oil, or you don’t."

Johns Hopkins called some lab studies "promising," but said clinical trials actually using humans were "mixed," with some showing benefits and others showing no improvement in symptoms.

More on essential oils What oils to use, how to use them and safety tips

When should you not use essential oils?

Those who are pregnant, nursing, taking medication and/or have a history of seizures should be wary of using essential oils, Hynicka says. Even if you're not, she recommends taking stock of what ailment you're hoping to solve by using essential oils — could it be better helped with a different form of treatment?

"I would recommend anyone using essential oils mention the reason and how they plan to use essential oils with their doctor or medical provider," Hynicka says, adding that they should be kept away from children and pets.

More: Can smelling candles actually make you sick?

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Essential Oil Science

Is there scientific validation for using essential oils.

Essential oils have been used for over a thousand years, but we are just scratching the surface of their potential. In the past, knowledge of essential oils was solely based off anecdotal experience.

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What is the science behind essential oils.

Each bottle of essential oil contains a unique blend of chemical constituents. These compounds are volatile and organic, meaning they quickly evaporate and their chemical structures are primarily composed of carbon atoms. Constituents can produce powerful effects through their interaction with cellular targets. Some constituents can attach to receptors located on the outside of a cell to influence changes within it, while others can readily pass through the cellular membrane and bind to enzymes, proteins, and even DNA. Understanding how essential oils induce beneficial effects through chemical interactions can lead to a renewed sense of confidence in their use and inspire new opportunities for application in daily life.

doTERRA's dedication to purity is unwavering.

Every drop of essential oil is a testament to our commitment to providing the highest quality products. Through rigorous sourcing practices, we ensure that our essential oils are derived from plants in their natural habitats.

Our Certified Pure Tested Grade (CPTG) protocol involves rigorous testing, including Gas Chromatography and Mass Spectrometry, to guarantee that each batch is free from contaminants and additives. This process is a cornerstone of our promise to offer 100% pure essential oils.

With transparency at the core of our values, you can trust that doTERRA products are synonymous with unparalleled quality and purity, allowing you to experience the true essence of nature.

Our Certified Pure Tested Grade (CPTG) protocol involves rigorous testing, including Gas Chromatography and Mass Spectrometry, to guarantee that each batch is free from contaminants and additives.

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Why doterra oils are so expensive, but worth every penny.

At doTERRA, we often encounter the question: "Why are your essential oils pricier than others?" The answer, in short, lies in our commitment to purity, sourcing, and overall quality.

• Unmatched purity: doTERRA's Certified Pure Tested Grade (CPTG) ensures that every bottle of oil you purchase is free from fillers, synthetic ingredients, and harmful contaminants. This stringent testing standard is unmatched in the industry. When you invest in doTERRA, you're paying for purity.
• Ethical sourcing: Our essential oils are sourced from over 40 countries, many of which are developing nations. Through our co-impact sourcing model, we establish direct partnerships with local farmers. This not only guarantees the highest quality oils but also supports sustainable farming practices and provides fair wages, ensuring a positive socio-economic impact on local communities.
• Potency and efficacy: The benefits of essential oils are directly related to their purity and quality. doTERRA's oils are potent, ensuring that users get the maximum benefit from each drop. This potency can actually lead to cost savings in the long run, as less oil is required for each application.

Impact Your Life and the Lives of People Worldwide

While the initial cost may be higher, the value of doTERRA's essential oils lies in their unrivaled quality, ethical sourcing, and potency. With doTERRA, you're not just buying an oil; you're investing in a better, healthier world.

doTERRA's dedication to making a positive impact extends beyond producing exceptional essential oils. Our Co-Impact Sourcing model focuses on creating sustainable livelihoods for farmers and communities around the world. By ethically sourcing raw materials from various regions, doTERRA helps improve local economies, provide fair wages, and support community development projects. This commitment to social responsibility inevitably influences product pricing, as the brand prioritizes people and planet alongside profit.

doTERRA Medical Journal Club

Welcome to an exclusive opportunity for healthcare professionals to expand their horizons and integrate holistic wellness into their practices. We are excited to invite licensed medical providers (including MDs, DOs, DCs, PAs, and NPs) to join our Monthly Essential Oil Journal Club.

This platform will allow practitioners to delve into the latest research on essential oils and wellness lifestyles, share insights, and explore integration methods into clinical practices. Each month, members can present findings, engage in enriching discussions, and contribute to the collective understanding of the health benefits of essential oils.

If you are passionate about holistic health and eager to explore the science behind essential oils, we encourage you to fill out this form and become part of an incredible community. Join us as we pioneer the bridge between modern medicine and natural wellness solutions.

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Arshad mixes an essential oils blend known as Agolin. Arshad and Brito are examining the effects of feeding Agolin to organic dairy cows, particularly how it impacts methane emissions, digestion, and milk production and quality.

Andre Brito (pictured) serves as an associate professor of dairy cattle nutrition and management at the University of New Hampshire.

Adeel Arshad, a Ph.D. student at UNH’s College of Life Sciences and Agriculture.

To measure enteric methane emissions, the NH Agricultural Experiment Station scientists use an automated head-chamber system called GreenFeed (pictured).

Key Research Finding

Supplementing Agolin Naturu , a blend of essential oils in the diet of organic dairy cows improves feed efficiency and reduces methane, which is produced through belching following enteric fermentation (a digestive process that occurs in the rumen, or the largest compartment of the cow’s stomach). Agolin has the additional benefit of increasing the production of milk and milk fat.

Sources of Greenhouse Gases within Agriculture

Within the agricultural sector, nitrous oxide and methane are the two primary greenhouse gases released. Nitrous oxide emissions primarily arise from soil management practices, including the application of synthetic and organic fertilizers, while methane is largely produced through enteric fermentation (i.e., the digestion process) in ruminants like cows and sheep, with the beef cattle industry being a larger methane emitter compared to the dairy sector. Source: EPA

Operating in markets that have notoriously thin and volatile profit margins, dairy farmers deeply care about the well-being of the animals they manage because happy cows are productive cows, and that could often mean the difference between being in the black or red. One reason that a cow may have lower milk production is an inefficiency digesting its feed—an outcome that’s accompanied by cows’ releasing more methane, especially for pasture-grazing animals that consume legumes and grass. New research from New Hampshire Agricultural Experiment Station (NHAES) scientist Andre Brito is showing promise that adding a plant-based essential-oils blend known as Agolin Naturu in organic dairy cow feed can aid animals’ digestive process, not only increasing milk production and quality but helping New Hampshire’s agriculture be a solution to climate change by reducing the release of a heat-trapping gas into the atmosphere .

“There is limited research on the use of Agolin in the United States dairies, and we are not aware of any study conducted in organic dairy systems.”

“Feed additives used on organic dairy farms, like that at UNH and 14 others located across the Granite State, must meet stringent USDA guidelines ,” explained Brito, an associate professor of dairy cattle nutrition and management. “Agolin, with its blend of essential oils from wild carrot and coriander, meets these standards, but scientists have only just recently started studying its use on organic dairies. One of our goals with this research is to build upon that knowledge and support organic dairies in reducing their greenhouse gas emissions while increasing their production levels.”

Small and mid-sized dairies— characteristic of 96% of New Hampshire farms —often benefit the most from research into maximizing production, as these farms have smaller profit margins and comparatively higher equipment costs than larger dairies. Additionally, there are unique opportunities to reduce enteric methane emissions in these farms through improved forage quality and use of feed additives to reduce their carbon footprint.

“There is limited research on the use of Agolin in the United States dairies, and we are not aware of any study conducted in organic dairy systems,” said Muhammad Adeel Arshad, a UNH College of Life Sciences and Agriculture Ph.D. student co-leading this research. “With cows in confinement, farmers can control the amount and type of feed they fed to their cows, but grazing cows select their most preferred grasses and legumes while on pasture. Therefore, there is a need to evaluate Agolin efficacy as cows transition from confinement to grazing.”

Brito and Arshad began studying the effects of Agolin on organic dairy cows at UNH in the spring of 2023. They designed a study in which organic Jersey cows were each fed 1 gram of Agolin per day for five weeks during confinement (i.e., when not at pasture) following winter-feeding schedules, and for five subsequent weeks when cows began to access to pastureland.

Additionally, the study was purposely conducted during the herds’ transition from an indoor, winter-feeding schedule to an outdoor, pasture-feeding schedule (which typically runs from April through September) due to changes that occur in organic cows’ microbial populations, which can affect milk production, as the cows acclimate to new conditions and food sources. Furthermore, scientists believe that this seasonal change in diet also influences methane emissions, resulting in greater methane production as the cows begin more pasture grazing.

“Our research investigates the continuous effect of Agolin on methane emissions and milk production as the cows transition from indoor to outdoor feeding,” explained Arshad. “We will be able to share with farmers when Agolin should be added to the cows’ diet to maximize its effects on methane emissions and milk production.”

According to Brito and Arshad, preliminary results already look promising and show that Agolin improved milk production by 6.5% and reduced the methane intensity, or amount of methane produced per pound of energy corrected milk, by 6%. The production of milk fat also increased, while the milk somatic cell count (an indicator of milk quality) reduced, with the Agolin feed.

For Brito and Arshad, a long-term goal of this research is to improve the capacity of dairy producers in New England and across the United States to market high-quality, environmentally sustainable milk while maximizing profits for small farms. This research effort—conducted at one of the two research dairy farms at the NHAES—is part of large-scale collaboration with 16 other research dairies at agricultural experiment stations across the United States is key to ensuring the success of that goal and the resiliency of U.S. dairy producers. Research efforts like this one ultimately show that improved production of milk and milk fat with reduced carbon footprint can help farmers to make informed decisions about the use of feed additives in their family operations.

This material is based on work supported by the NH Agricultural Experiment Station through joint funding from the USDA National Institute of Food and Agriculture (under Hatch award numbers 7005829) and the state of New Hampshire.

Written By:

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What is ‘oil pulling,’ and is it good for your teeth?

Consumer Reports has no financial relationship with any advertisers on this site.

The practice of oil pulling involves swishing a small amount of cooking oil in your mouth with the goal of improving oral health. Originally an ancient ayurvedic technique , it has drawn growing interest more recently, racking up millions of views on TikTok .

Because oils such as coconut, sunflower and sesame are thought to have antimicrobial properties , swishing with these oils could, in theory, reduce the incidence of germ-related dental problems such as gingivitis and cavities.

Some research suggests oil pulling might have limited benefits for certain aspects of oral health. Yet experts caution it shouldn’t be used in place of standard dental hygiene practices such as brushing and flossing, and people should never opt for oil pulling as a replacement for evidence-based treatments for serious dental issues.

The evidence on oil pulling

The research on oil pulling is mixed, and there aren’t enough large-scale scientific trials to demonstrate that it can effectively promote dental health. One meta-analysis reported that while oil pulling may indeed reduce bacteria in the mouth, it doesn’t have a significant effect on plaque or gingivitis. Another analysis compared oil pulling to rinsing with an antimicrobial prescription mouthwash, chlorhexidine, and found that chlorhexidine was superior to oil pulling for reducing plaque and bacteria in the mouth. The overall quality of evidence was low, however.

Some dental trends, such as brushing with charcoal and lemon juice for whitening purposes, could pose significant harm to your teeth. By contrast, swishing food-safe oil in your mouth is unlikely to be detrimental, says Matthew J. Messina, a consumer adviser spokesperson for the American Dental Association and an assistant professor and clinic director at Ohio State Upper Arlington Dentistry in Columbus, Ohio.

“If a patient with excellent oral hygiene and healthy gums and teeth tells me they’re oil-pulling, there’s no reason to stop doing it,” he says.

But oil pulling may be risky if it’s done as a replacement for other dental best practices, such as brushing, flossing and visiting the dentist. While oil pulling may reduce overall bacteria in the mouth, Messina says, it’s likely not as effective as mechanical brushing in removing plaque from teeth. And swishing oil around probably won’t reach tight crevices between your teeth, where gingivitis-causing bacteria often linger. That’s why flossing is essential.

It’s also not a good idea to treat gum disease or cavities with oil pulling. “You can cause more harm than good by trying to treat things on your own,” says Amelia E. Hartzell, a dentist with UTHealth Houston School of Dentistry and UT Dentists. “It’s a better idea to talk to your dentist, who can help you.” Infections in your mouth, Messina adds, should be treated by a medical professional, who may suggest prescription antibiotics.

Dental best practices

It may sound boring, but brushing and flossing are the most reliable ways to maintain oral health. If you want to mix it up, you can throw in a fluoride mouthwash , which studies show can reduce inflammation and bacteria if used properly.

Hartzell recommends twice-daily brushing with a soft-bristled brush and fluoride toothpaste, which strengthens the porous outer layer of your teeth to prevent cavities. Angle your brush toward your gum line and brush in small circles for two minutes. “An electric toothbrush can help with the motion, and all you have to do is angle it,” says Hartzell. Aim to floss at least once a day to remove soft food debris, or plaque, between teeth before it calcifies and causes gum disease or cavities.

Diet, Hartzell says, can also play a role in maintaining dental health. Cavity-causing bacteria feed on sugar, so try to reduce your overall sugar intake. When you do eat sugar, wait about 30 minutes before you brush your teeth to let your saliva dissipate the sugar on your teeth; Hartzell says sugar breaks down enamel, and brushing too soon could wear down your enamel faster. Carbonated beverages — even ones that don’t contain sugar — are known to break down enamel, which can increase your risk of cavities and cause teeth sensitivity.

See your dentist on a regular basis, too. While Messina says most people should get a dental exam and cleaning twice a year, people with dental problems may need to visit more often for treatment and preventive care. Either way, your dentist is the best resource for how to keep your mouth healthy. “Find a dental home, a place where you’re comfortable and get good, evidence-based advice,” says Messina. And if you love oil pulling, it’s unlikely to cause any harm — but you can also consider saving the cooking oils for cooking.

Copyright 2024, Consumer Reports Inc.

Consumer Reports is an independent, nonprofit organization that works side by side with consumers to create a fairer, safer, and healthier world. CR does not endorse products or services, and does not accept advertising. Read more at ConsumerReports.org .

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• v.5(5); Sep-Oct 2015

Essential oils, their therapeutic properties, and implication in dentistry: A review

Namrata dagli.

Ethics Committee, Care Institute of Medical Sciences, Ahmedabad, Gujarat, India

Rushabh Dagli

1 Department of Public Health Dentistry, Vyas Dental College and Hospital, Jodhpur, Rajasthan, India

Rasha Said Mahmoud

2 Department of Preventive Dental Science, Alfarabi Colleges, Riyadh, Saudi Arabia

Kusai Baroudi

Background:.

Antibacterial treatments currently used for treatment cause several side effects, and bacterial resistance to the antibiotics is also increasing. Therefore, there is need to find better alternatives. Essential oils (EOs) have been used for treatment of various ailments since ancient times and have gained popularity over the years. Safety and efficacy of EOs have been proved by several clinical trials. This review gives an overview on the EOs, their uses, and adverse effects.

Materials and Methods:

A literature search was performed in the PubMed for clinical trial studies and review articles on EOs published up to February 2015. The search was performed during March 2015. The following keywords were used: “Lavender essential oil,” “cinnamon oil,” “clove oil,” “eucalyptus oil,” “peppermint oil,” “lemon EOs,” and “tea tree oil.”

Total 70 relevant articles were found in PubMed database. After screening of abstracts, 52 articles were selected to be included in the present review.

Conclusion:

On the basis of the available information, it can be concluded that EOs have the potential to be developed as preventive or therapeutic agents for various oral diseases, but further clinical trials are required to establish their safety and efficacy.

INTRODUCTION

According to the World Oral Health Report, despite great improvements in oral health in several countries, oral health problems still persist, particularly among underprivileged groups in both developing and developed countries.[ 1 ] Dental caries and periodontal diseases are identified as the most important among oral health problems globally. Oral diseases adversely affect the general health too. Quality of life and the working capacity of an individual are also affected.[ 2 ]

The antibacterial agents that are currently used for treatment of oral health problems are reported to cause several side effects such as diarrhea, vomiting, etc., Increasing bacterial resistance to the drugs is also a major concern. Because of the adverse effects, increasing bacterial resistance, and high cost associated with the standard therapeutic procedure, there is a need to explore new therapeutic agents and conduct further clinical research on traditional medicines obtained from various plant sources.

Many traditionally used medicines for treating infections have been studied again, and clinical trials are being done to establish their efficacy and possible side effects. One of these natural medicines is essential oils (EOs).[ 3 , 4 ] In the recent years, there has been an increased interest toward EOs.

Approximately 3000 Eos are known till now.[ 5 ] EOs are one of the plant extracts that have been used for treatment of various medical and dental problems since ancient times. These are secondary metabolites produced by various medicinal plants and possess antibacterial, antifungal, and antioxidant properties.[ 6 , 7 , 8 ]

The purpose of this systematic review is to analyze the published data related to the EOs. A number of studies have been conducted to prove the therapeutic properties of various EOs, but very few reviews have been published on their implication in dental treatment. The review gives an overview on the EOs, their therapeutic properties, and adverse effects.

MATERIALS AND METHODS

To identify relevant literature, an electronic search was performed on PubMed database.

Titles and abstracts were screened. Only articles related to lavender oil, eucalyptus oil, clove oil, cinnamon oil, and lemon EOs have been included in this review. Studies related to several other EOs were excluded. Total 52 articles found relevant were selected for this review.

EOs and their composition

EOs are secondary metabolites of plants whose constituents are basically a complex mixture of terpenic hydrocarbons, especially monoterpenes and sesquiterpenes, and oxygenated derivatives such as aldehydes, ketones, epoxides, alcohols, and esters.[ 9 ] EOs greatly differ in their compositions. Even the composition of EOs extracted from the plants of same species differ in different geographic locations.[ 10 ] Composition also depends on the maturity of the plant from which the EOs are extracted.[ 10 , 11 ]

Mechanism of action

The mechanisms of action of EOs are dependent on their chemical composition and the location of one or more functional groups on the molecules present in them.[ 12 ]

Membrane damage is proposed to be the main mechanism of action.[ 13 ] Solubility of EOs in the phospholipid bilayer of cell membranes seems to have an important role in their antimicrobial activity. Clove oil has reported to reduce the quantity of ergosterol which is found specifically in fungal cell membrane.[ 14 ] Terpenoids in EOs have been found to interfere with the enzymatic reactions of energy metabolism.[ 15 ]

Essential oils that have potential to be used in oral disease prevention and treatment are discussed subsequently.

Lavender oil

Composition.

Major components found are linalool, linalyl acetate, 1,8-cineole, B-ocimene, terpinen-4-ol, l-fenchone, camphor, and viridiflorol.[ 10 , 16 ] However, the relative level of each of these constituents varies in different species. Lavender oil, obtained from the flowers of Lavandula angustifolia (Family: Lamiaceae) by steam distillation, is chiefly composed of linalyl acetate (3,7-dimethyl-1,6-octadien-3yl acetate), linalool (3,7-dimethylocta-1,6-dien-3-ol), lavandulol, 1,8-cineole, lavandulyl acetate, and camphor.

The activity of linalool reflects that of the whole oil, indicating that linalool may be the active component of lavender oil.[ 13 ]

Therapeutic properties

• Antimicrobial activity: EOs extracted from Lavandula stoechas L. exhibit good antimicrobial activities against most of the bacteria, filamentous fungi, and yeasts. In the study of Benabdelkader et al ., minimum inhibitory concentrations were found to be ranging from 0.16 to 11.90 mg/ml.[ 10 ] It also shows antipseudomonal activity[ 16 ]
• In vitro study on the antibacterial activity of the EO of Lavandula coronopifolia against antibiotic-resistant bacteria suggested its bactericidal effect[ 17 ]
• Anxiolytic: Lavender EO is reported to reduce stress, anxiety, and improve mood when inhaled or orally administered.[ 18 , 19 ] It is not very effective in cases of high anxiety[ 20 ]
• Antifungal: EOs of Lavandula luisieri show an inhibitory effect on yeast, dermatophyte, and Aspergillus strains.[ 21 ] Lavandula viridis is reported to have fungicidal effect. Cryptococcus neoformans is the most sensitive fungus, followed by Candida species.

Eucalyptus oil

The main component is 1,8-cineole followed by cryptone, α-pinene, p -cymene, α-terpineol, trans-pinocarveol, phellandral, cuminal, globulol, limonene, aromadendrene, spathulenol, and terpinene-4-ol.[ 22 ]

• Antimicrobial effect: Antimicrobial activity was found to be related to the synergic effects between major and minor components rather than the concentration of a single component.[ 22 ] EO of the leaves of Eucalyptus globulus has antimicrobial activity against Gram-negative bacteria ( Escherichia coli ) as well as Gram-positive bacteria ( Staphylococcus aureus ).[ 23 ] Studies done on eight eucalyptus species show that Eucalyptus odorata oil possesses strong cytotoxic effect and also antibacterial effect against S. aureus , Haemophilus influenzae , Staphylococcus pyogenes , and Staphylococcus pneumonia . Eucalyptus bicostata and Eucalyptus astringens showed antibacterial effects[ 22 ]
• Anti-inflammatory effect: Immunoregulatory agent: The study of Serafino et al . demonstrates that eucalyptus EO can stimulate the innate cell-mediated immune response suggesting its use as adjuvant in immunosuppression, in infectious disease, as well as in tumor chemotherapy.[ 24 ]

Peppermint oil

Peppermint ( Mentha piperita ) oil is one of the most popular and widely used EOs. In the EO from M. piperita , menthol is identified as the major compound, followed by menthyl acetate and menthofuran.[ 25 ]

• Antibacterial: Peppermint oil shows an inhibitory effect on the proliferation of staphylococci[ 26 ]
• Antifungal: Studies show that EOs exhibit fungistatic and fungicidal activities against both the standard and clinical strains of Candida species at concentrations ranging from 0.5 to 8 μL/mL. EOs exhibit similar antifungal effect against the azole-resistant and azole-susceptible strains[ 25 ]
• Antibiofilm: Biofilm inhibition in fungal strains helps to decrease pathogenesis and drug resistance. Studies show that EO inhibits the biofilm formation of Candida albicans completely up to 2 μl/ml in a dose-dependent manner.[ 25 ]

Melaleuca alternifolia (Myrtaceae)

It is also known as Tea Tree Oil (TTO). Its composition shows terpinen-4-ol, γ-terpinene, p -cymene, α-terpinene, 1,8-cineole, α-terpineol, and α-pinene.[ 27 ]

• Antibacterial: In a clinical trial, the melaleuca gel was found to possess an inhibitory effect on various bacterial colonies and dental biofilm.[ 28 ] It shows strong antibacterial action against oral pathogens[ 29 ]
• Antifungal activity: Melaleuca alternifolia possesses antimycotic activity, terpinen-4-ol being its most effective component.[ 30 ]

Mostly, it contains almost exclusively terpenes and oxygenated terpenes.[ 31 ]

Therapeutic activity shows antifungal potential against three Candida species ( C. albicans , Candida tropicalis , and Candida glabrata ). Lemon EO is suggested to be used as an effective remedy against candidiasis caused by C. albicans .[ 31 , 32 ]

Main constituents found in the clove bud oil are the phenylpropanoids eugenol, eugenyl acetate, carvacrol, thymol, cinnamaldehyde, β-caryophyllene, and 2-heptanone, when analyzed by gas chromatography.[ 33 , 34 ]

Medicinal properties

Eugenol is well-known for its therapeutic properties and is widely used in dentistry.

• Antioxidant: When tested against tert -butylated hydroxytoluene, EO exhibited a very strong radical scavenging activity[ 33 ]
• Antifungal: It possesses antifungal activity.[ 33 ] Clove oil and its main content eugenol also reduce the quantity of ergosterol, which is a specific component of fungal cell membrane. Germ tube formation by C. albicans is also inhibited[ 14 ]
• • Antibacterial: It was found to possess inhibitory effect on multi-resistant Staphylococcus spp.[ 34 ]

Cinnamon oil

The volatile oils obtained from the bark, leaf, and root barks vary significantly in chemical composition. Three of the main components of the EOs obtained from the bark of Cinnamomum zeylanicum are trans -cinnamaldehyde, eugenol, and linalool, which represent 82.5% of the total composition. Cinnamaldehyde is the major constituent of cinnamon EO, and studies show that it is the most active component too.[ 35 ]

Antimicrobial effect: Inhibitory effect on the growth of various isolates of bacteria including Gram-positive, Gram-negative, and fungi.[ 36 ]

Antimutagenic: It has antimutagenic potential against spontaneous mutations in human cells.[ 37 ] Furthermore, the study of Cabello et al . performed in animals shows that oral administration of cinnamaldehyde (CA) exerts significant anti-melanoma activity.[ 38 ]

Besides these activities, studies suggest that cinnamomum zeylanicum (CZ) has antiparasitic, antioxidant, and free radical scavenging properties.[ 39 ]

Implications in dental practice

Potential implications of EOs have been described below and the information is consolidated in Table 1 .

Essential oils and their potential implications in dentistry

It can be used in dental clinics to reduce patients’ anxiety. It is found to be useful as an anxiolytic agent when used in waiting area.[ 18 , 20 ] The study performed by Zabirunnisa showed statistically significant reduction in anxiety scores when the fragrance of lavender oil was used at the reception area. It is also helpful during surgical procedures, as it has been shown to reduce the pain of needle insertion.[ 19 ]

It shows an inhibitory effect on oral pathogens like Lactobacillus acidophilus , which makes this suitable to be used as an anticariogenic agent.[ 44 ]

Eugenol oil is used widely in dentistry. It is active against oral pathogens associated with dental caries and periodontal disease.[ 45 ] Studies done on five EOs (TTO, lavender oil, thyme oil, peppermint oil, and eugenol oil) against four common oral pathogens ( S. aureus , Enterococcus faecalis , E. coli , and C. albicans ) showed significant inhibitory effect of eugenol oil, peppermint oil, and TTO. Among them, eugenol oil showed antimicrobial activity at the lowest concentration level.[ 41 ]

TTO and some of its individual components, specifically terpinen-4-ol, exhibit strong antimicrobial efficacy against fungal biofilms. TTO can be a solution for the increasing resistance of C. albicans to established antifungal drugs. It can be used to treat oral candidiasis[ 42 ] and is suitable for use in prophylactic oral hygiene products. The study performed by Ramage et al . shows that it is more appropriate and safe to use terpinen-4-ol, the major component of TTO, than TTO itself.[ 46 ]

A Phase I clinical trial conducted on cinnamon EO concluded that it is safe to be used in healthy patients with dentures for the treatment of oral candidiasis.[ 40 ]

Lemon EO is suggested to be used as an effective remedy against candidiasis caused by C. albicans .[ 32 ]

Combination of EOs

Combining EOs and antibiotics can reduce antibiotic resistance in multidrug-resistant bacteria. Peppermint, cinnamon bark, and lavender EOs were found to be antibiotic resistance-modifying agents, when used in combination with piperacillin.[ 43 ]

Studies not supporting the use of EOs

Several studies support the benefits of EOs, but some studies raise questions about their efficacy.

A study in which 0.2% chlorhexidine rinse and an EO mouth rinse were compared for their efficacy showed that EOs are effective only for very short duration, i.e., 2–3 h, and concluded that use of chlorhexidine is preferable over EOs.[ 47 ]

A study done on EOs to measure their efficacy when used as a coolant concluded that there was no benefit over water during ultrasonic root debridement for the treatment of chronic periodontitis.[ 48 ]

Adverse effects caused by EOs

Natural medicines are not always free of side effects. Adverse effects are also reported with EOs. In the study of Millet et al ., commercial preparations of essences of sage, hyssop, thuja, and cedar have been reported to cause neurotoxicity and human intoxication, of which tonic–clonic convulsions formed the major symptom.[ 49 ]

According to a review by Posadzki et al ., mild to severe adverse effects including fatality can be caused by EOs like lavender, peppermint, TTO, and ylang-ylang when used in aromatherapy. Most common adverse effect among them was dermatitis.[ 22 ]

Toxicological tests are often lacking for traditional medicines. Therefore, further clinical trials are required to exclude the possibility of side effect and poisoning.

Limitations

Only seven EOs that are found to be used commonly are included in this review. The review is subjected to publication bias as it is written on the basis of published literature. Only English language articles were referred. Article search was performed only in one database, PubMed.

CONCLUSIONS

As described in this review, there is considerable evidence that EOs have potential to be developed as preventive or therapeutic agents for various oral diseases. Although several other potential uses of EOs have been described[ 50 ] and many claims of therapeutic efficacy have been validated adequately by either in vitro testing or in vivo clinical trials, still there is need for conducting further research to establish the safety and efficacy of these EOs before including them in clinical practice. If used properly, they may prove very useful in dental therapy and may contribute in improving the quality of dental treatments.

In particular, clinical trials that confirm the therapeutic potential of EOs in vivo and address issues such as adverse effects, toxicity, and their interaction with other drug molecules would be of great value.

Source of Support: Nil

Conflict of Interest: None declared.