Despite the popularity of aromatherapy, data on efficiency is scanty, and potential mechanisms are controversial. This randomized controlled study investigated the psychological, autonomic, endocrine, and immune effects of one exposed to a calming odor (lavender), one stimulant odor (lemon), and no-odor regulation (water).
Before and after a stressor (cold pressor), 56 healthy men and women were exposed to each of the odors throughout three separate visits. To assess the effects of expectations, participants were randomized and were given no information on the aromas they would smell. Self-reporting and unobtrusive mood tests offered clear evidence that lemon oil consistently improves positive mood compared with water and lavender. In addition, norepinephrine levels following the cold pressor remained elevated compared with water or lavender when subjects smelled lemon. Following inhalation of vapor, DTH responses to candida were larger than lemon or lavender. Odors have not consistently altered the development of IL-6 and IL-10, salivary cortisol, heart rate or blood pressure, skin barrier repair after tape stripping, or cold presser pain scores.
The full research is available at US National Library of Medicine, National Institutes of Health, or here