Digging through the research on the National Institutes of Health website, Pub Med (see http://www.ncbi.nlm.nih.gov/pubmed/) can really be fruitful for scientific data on the effects of essential oils. A great many studies have been published over the last ten years validating the use of essential oils in many realms of natural health, from immunity and infectious illness to wound healing and pain relief, to sleep, mood and cognitive effects. Here are a few studies noting measurable changes in brainwaves upon inhalation of aromas.

Now it's not surprising that essential oils elicit changes in brainwaves - really this happens with anything we perceive with our sense organs: touch, sight, hearing, taste OR smell. What's interesting is that the brainwaves are in-fact measurably different depending on the oil inhaled. Further, the brainwave response was also dependent on the time of day and type of action the subjects were performing when inhaling the oils. Some oils seemed appreciated during physical work, some during mental work, some before work and some after.

The first study describes changes in Alpha brainwaves. These waves are associated with a relaxed, steady, perhaps even 'contemplative' state (one website described most of America as 'alpha wave challenged'!) Lavender essential oil produced the most significant, fairly rapid increase in Alpha wave activity.

The second study describes differences between oils which may be considered relaxing, uplifting or mentally stimulating before and after both physical and mental work. Some oils tested produced very statistically significant results: In summary, try Orange before physical work and Cypress after. Try Basil before mental work and Juniper afterward.

Study: Effects of inhalation of essential oils on EEG activity and sensory evaluation.

Masago R, Matsuda T, Kikuchi Y, Miyazaki Y, Iwanaga K, Harada H, Katsuura T. Graduate School of Science and Technology, Chiba University.

The purpose of this study was to investigate EEG changes in subjects directly after inhalation of essential oils, and subsequently, to observe any effect on subjective evaluations. EEG and sensory evaluation were assessed in 13 healthy female subjects in four odor conditions. Four odor conditions (including lavender, chamomile, sandalwood and eugenol) were applied respectively for each subject in the experiment. The results were as follows. 1) Four basic factors were extracted from 22 adjective pairs by factor analysis of the sensory evaluation. The first factor was "comfortable feeling", the second "cheerful feeling", the third "natural feeling" and the fourth "feminine feeling". In the score of the first factor (comfortable feeling), the odors in order of high contribution are lavender, eugenol, chamomile and sandalwood. 2) Alpha 1 (8-10 Hz) of EEG at parietal and posterior temporal regions significantly decreased soon after the onset of inhalation of lavender oil. The change after inhalation of sandalwood was not significant. These results showed that alpha 1 activity significantly decreased under odor conditions in which subjects felt comfortable, and showed no significant change under odor conditions in which subjects felt uncomfortable. These results suggest a possible correlation between alpha 1 activity and subjective evaluation.

Study: Alteration of perceived fragrance of essential oils in relation to type of work: a simple screening test for efficacy of aroma.

Sugawara Y, Hino Y, Kawasaki M, Hara C, Tamura K, Sugimoto N, Yamanishi Y, Miyauchi M, Masujima T, Aoki T. Department of Health Science, Hiroshima Prefectural Women's University, Japan.

The perceptional change of fragrance of essential oils is described in relation to type of work, i.e. mental work, physical work and hearing environmental (natural) sounds. The essential oils examined in this study were ylang ylang, orange, geranium, cypress, bergamot, spearmint and juniper. In evaluating change in perception of a given aroma, a sensory test was employed in which the perception of fragrance was assessed by 13 contrasting pairs of adjectives. Scores were recorded after inhaling a fragrance before and after each type of work, and the statistical significance of the change of score for 13 impression descriptors was examined by Student's t-test for each type of work. It was confirmed that inhalation of essential oil caused a different subjective perception of fragrance depending on the type of work. For example, inhalation of cypress after physical work produced a much more favorable impression than before work, in contrast to orange, which produced an unfavorable impression after physical work when compared with that before work. For mental work, inhalation of juniper seemed to create a favorable impression after work, whereas geranium and orange both produced an unfavorable impression then. From these studies, together with those conducted previously with lavender, rosemary, linalool, peppermint, marjoram, cardamom, sandalwood, basil and lime, we thus concluded that the sensory test described here might serve not only as a screening test for efficacy of aroma but also as a categorized table for aroma samples which can act as a reference to each other.