What Does the Research Say About Essential Oils?
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?
A significant body of research on essential oils has been conducted by the food, flavoring, cosmetics, and tobacco industries. They are most interested in the flavor, mood alteration, and preservative qualities of essential oils. Some of these companies have also conducted extensive research on the toxicity and safety of essential oils.
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?
There are some unique 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
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.
References and current studies
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.
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, Jan, 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. Journal 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, Jul-Aug, 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, June, 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, Feb 1, 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 sis-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.