Numerous studies on the topical antibacterial effects of essential oils have been published; most have found the oils to have significant antimicrobial activity.[1]

Studies on rats in Europe and Japan have shown that exposure to various odors can result in stimulation or sedation, as well as changes in behavioral responses to stress and pain. A study [2] on the sedative effects of essential oils and other fragrance compounds (mostly individual chemical components of the oils) on rat motility showed that lavender oil (Lavandula angustifolia Miller [synonyms: Lavandula spicata L.; Lavandula vera DC.]) in particular had a significant sedative effect, and several single-oil constituents (as opposed to whole essential oils) had similarly strong effects. The authors do not comment on the presumed mechanism for this effect, though they suggest that the difference in results between the different oils (some of which were found to be stimulating, some sedative) is related to the “different chemical structures of the compounds…and functional groups…indicating the essential role of the volatility of the fragrance compounds and its bioavailability.” The differences in bioavailability are ascribed to different levels of lipophilia, with the more lipophilic oils producing the most sedative effects. The researchers also found significant plasma levels of the fragrance compounds after inhalation, suggesting that the effects of aromatherapy result from a direct pharmacological interaction rather than an indirect central nervous system relay.

Other studies have investigated the effects of aromatherapy on rats’ behavioral and immunological responses to painful, stressful, or startling stimuli. In two European studies, rats exposed to pleasant odors during painful stimuli exhibited decreased pain-related behaviors, with some variation in response between the sexes.[3,4] Two studies from Japan showed an improvement in immunological and behavioral markers in rats exposed to fragrances while under stressful conditions.[5,6]

References

1. Aridoğan BC, Baydar H, Kaya S, et al.: Antimicrobial activity and chemical composition of some essential oils. Arch Pharm Res 25 (6): 860-4, 2002.  [PUBMED Abstract]
   
   
2. Buchbauer G, Jirovetz L, Jäger W, et al.: Fragrance compounds and essential oils with sedative effects upon inhalation. J Pharm Sci 82 (6): 660-4, 1993.  [PUBMED Abstract]
   
   
3. Aloisi AM, Ceccarelli I, Masi F, et al.: Effects of the essential oil from citrus lemon in male and female rats exposed to a persistent painful stimulation. Behav Brain Res 136 (1): 127-35, 2002.  [PUBMED Abstract]
   
   
4. Jahangeer AC, Mellier D, Caston J: Influence of olfactory stimulation on nociceptive behavior in mice. Physiol Behav 62 (2): 359-66, 1997.  [PUBMED Abstract]
   
   
5. Shibata H, Fujiwara R, Iwamoto M, et al.: Immunological and behavioral effects of fragrance in mice. Int J Neurosci 57 (1-2): 151-9, 1991.  [PUBMED Abstract]
   
   
6. Fujiwara R, Komori T, Noda Y, et al.: Effects of a long-term inhalation of fragrances on the stress-induced immunosuppression in mice. Neuroimmunomodulation 5 (6): 318-22, 1998 Nov-Dec.  [PUBMED Abstract]
   
   

Glossary Terms

A substance that kills bacteria or stops them from growing and causing disease.

A substance that kills microorganisms such as bacteria or mold, or stops them from growing and causing disease.

A type of complementary and alternative medicine that uses plant oils that give off strong pleasant aromas (smells) to promote relaxation, a sense of well-being, and healing.

The ability of a drug or other substance to be absorbed and used by the body. Orally bioavailable means that a drug or other substance that is taken by mouth can be absorbed and used by the body.

The brain and spinal cord. Also called CNS.

The scented liquid taken from certain plants using steam or pressure. Essential oils contain the natural chemicals that give the plant its “essence” (specific odor and flavor). Essential oils are used in perfumes, food flavorings, medicine, and aromatherapy.

A pleasant, sweet odor.

The activity of the immune system against foreign substances (antigens).

In medicine, refers to the act of taking a substance into the body by breathing.

A plant with aromatic leaves and flowers that is a member of the mint family. Oil from the flowers has been used in some cultures to treat certain medical problems, to keep insects away, and to wash in. It is also used in aromatherapy. Perillyl alcohol, a substance found in lavender, is being studied in cancer prevention and treatment. The scientific name is Lavandula angustifolia. Also called English lavender and true lavender.

Able to dissolve, be dissolved in, or absorb lipids (fats).

A smell.

The clear, yellowish, fluid part of the blood that carries the blood cells. The proteins that form blood clots are in plasma.

A drug or substance used to calm a person down, relieve anxiety, or help a person sleep.

In statistics, describes a mathematical measure of difference between groups. The difference is said to be significant if it is greater than what might be expected to happen by chance alone. Also called statistically significant.

On the surface of the body.