Researchers found aromatherapy was no better than distilled water in relieving pain, boosting immune function, or altering stress hormone responses.

by John Gever, Staff Writer, MedPage Today 

Columbus, Ohio, March 7 — Aromatherapy was no better than distilled water in relieving pain, boosting immune function, or altering stress hormone responses, researchers here found.

After sniffing lemon oil, lavender, or distilled water, healthy volunteers showed almost no differences in a battery of psychological, physical, and laboratory evaluations, reported Janice K. Kiecolt-Glaser, Ph.D., of Ohio State University, and colleagues in the April issue of Psychoneuroendocrinology.

The only unambiguous positive effect the researchers found was that lemon oil genuinely lifted mood, according to an objective clinical evaluation as well as participants’ self-assessment, Dr. Kiecolt-Glaser said in an interview.

It was the sole finding in the study that supported claims by aromatherapy proponents for these products. Lemon oil is purported to have stimulant effects.

Lavender is billed as a relaxant, but it was undistinguishable from water according to nearly every evaluation in the study.

These findings held even among participants who frequently used aromatherapy before entering the study.

“The data from this randomized controlled trial are important because they directly address both potential mechanisms and clinical efficacy,” the researchers wrote.

Said William Malarkey, M.D., another Ohio State researcher who worked on the study, “This is probably the most comprehensive study ever done in this area.”

The researchers studied 56 healthy volunteers with a mean age of 24.4 (SD 6.1) who inhaled each of the three test substances on separate lab visits.

They had passed an initial “smell test” intended to weed out people with impaired olfactory function. They also underwent a structured interview on their prior experiences with aromatherapy.

The study sessions began by placing a heparin well in one arm of each participant followed by a standard breakfast. They completed a series of questionnaires to establish baseline mood and emotional values. Blood samples were drawn and heart rate and blood pressure measurement began.

Half the participants were then told what odor they would smell that day and what effects they could expect. The rest were kept blind. Investigators performing objective assessments were always blinded to the odors under study.

The following physiological responses were evaluated in addition to heart rate and blood pressure:

  • Delayed hypersensitivity to Candida
  • Blastogenesis in peripheral blood leukocytes
  • Stimulated IL-6 and IL-10 production from peripheral blood leukocytes
  • Salivary cortisol, epinephrine, and norepinephrine levels
  • Skin barrier healing after standardized tape stripping

Emotional responses were measured with the Stroop test twice during odor exposure and mood was evaluated three times with the Positive and Negative Affect Schedule. In addition, their responses to the International Affective Picture System and a thought-listing procedure were used to measure mood indirectly.

Participants also recorded intensity of pain sensations associated with immersing their feet in ice water for one minute.

Odor exposure lasted for 3.25 continuous hours, followed by a short lunch break and removal of the heparin well, and then another odor exposure lasting 30 minutes.

With few exceptions, Dr. Kiecolt-Glaser and colleagues found no consistent, significant differences in any of these measurements between distilled water, lemon oil, and lavender.

The chief exception was in lemon oil’s effect on mood. Whereas positive affect scores declined from 24 points at baseline to 22 points after both lavender and water, scores increased to nearly 25 points post-odor with lemon oil (P<0.004).

Also, norepinephrine levels following the ice-water bath remained high when the odor was lemon oil, whereas levels of this stress hormone declined when participants were exposed to lavender or water.

The only other significant difference among odors was seen in the delayed hypersensitivity test, which found a larger effect with water relative to either active agent. This finding suggests that lemon oil and lavender inhibited the immune response. Both lavender and lemon oil have been touted as an immune booster, Dr. Kiecolt-Glaser and colleagues noted.

The researchers found only one difference in responses between participants who were told what to expect and those who were not. Lymphocyte proliferation was enhanced with lavender (but not lemon oil) relative to water among the “primed” participants but not among those kept blind. All other responses were similar regardless of expectancy.

Dr. Kiecolt-Glaser and colleagues also analyzed the results in 16 participants who had reported using aromatherapy — defined as scents used for reasons other than enjoyment — at least monthly before entering the study.

Their physiological and subjective responses were no different from those of other participants, the researchers found.

The study was funded by the National Center for Complementary and Alternative Medicine at the National Institutes of Health (NIH), an NIH Training Grant, a General Clinical Research Center Grant MO1-RR-0034, an Ohio State Comprehensive Cancer Center Core Grant. 

The authors reported no potential conflicts of interest.  Discuss>> 

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Published: March 07, 2008
Reviewed by Robert Jasmer, MD; Associate Clinical Professor of Medicine, University of California, San Francisco 


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Source reference:

Kiecolt-Glaser J, et al “Olfactory influences on mood and autonomic, endocrine, and immune function” Psychoneuroendocrinology 2008; 33: 328-39.