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While there is scant evidence for the efficacy of aromatherapy in treating disease, it is well known that certain fragrances, such as mint, lavender, and jasmine, can influence stress-induced psychosomatic disorders. Now, a near infrared spectroscopic study of the brain and facial skin secretion response to long-term use of a specific fragrance could provide useful clues about the underyling neurophysiological mechanism of such changes and could one day lead to a novel acne treatment. Several animal studies have suggested that olfactory stimulation with fragrances can improve stress-induced immune suppression, explain the authors of research published to be in the journal Neuroscience Letters. Studies on humans too have demonstrated that the smell of lavender and rosemary can reduce levels of the stress hormone cortisol measured in saliva. "These results indicate that fragrances can improve various stress-induced psychosomatic disorders; however, the neurophysiological mechanisms of their effects remain unclear," they say. Now, the team, Masahiro Tanida and Masako Katsuyama of the Bioengineering Research Laboratories, at the Shiseido Life Science Research Center, in Yokohama, working with Kaoru Sakatani of the Department of Neurological Surgery, at Nihon University School of Medicine, in Tokyo, Japan, have evaluated the effect of fragrance on secretion of sebum from facial skin and associated activity in the stress-induced prefrontal cortex (PFC) of the brain using NIR spectroscopy. The researchers point out that the skin complaint acne vulgaris, commonly known as acne, is thought to have a mental stress component in its aetiology. Tanida and colleagues explain that mental stress activates the hypothalamic-pituitary-adrenal (HPA) axis. This triggers hormone release and stimulates growth of sebaceous glands. The HPA axis is thought to be regulated in particular by the right-side of the prefrontal cortex (PFC). Indeed, activity in the right PFC has been shown, using functional MRI, to correlate mental stress tasks with changes in levels of salivary cortisol levels. The Japanese team has turned to a powerful alternative to fMRI for studying brain activity, near-infrared spectroscopy. Previously, the team demonstrated that subjects who have right-dominant PFC activity during mental stress tasks also secrete more facial sebum. This suggests that such people are sensitive to mental stress associated with hyperactivity of the HPA axis, the researchers explain. NIR, the researchers knew, could reveal haemoglobin concentration changes in the brain while volunteers carried out a mental arithmetic task. The volunteers were all college-level, healthy, female students around the age of 22 and all right-handed. The group of 31 were divided randomly in two - a fragrance group and a control group. The researchers found a significant positive correlation between the level of sebum secretion before the volunteers did the test and the differences in oxyhaemoglobin (oxyHb) levels between the right and left of this region of the brain. They then selected those subjects who had the highest levels of sebum secretion and right-dominant brain activity and administered fragrance - a pleasant, floral green tone - for four weeks and tested them again. They found that sebum secretion fell significantly. Moreover, left-oxyHb decreased significantly. The researchers say this indicates that the dominant side of the stress-induced PFC activity changed from the right to left side. Left-oxyHb and sebum secretion changed negligibly in the control group. "Our results suggest that administration of fragrance reduced the level of sebum secretion by modulating the stress-induced PFC activity," say the researchers in the journal Neuroscience Letters. "The PFC may be involved in the neurophysiological mechanism of fragrance effects on systemic response to mental stress," they add. The researchers explain that their experiment has several limitations. First, is that the sample group was small. Moreover, the volunteers were all young females so the effects of age or gender on PFC were not investigated. "This was a pilot study designed to evaluate the possibility that fragrances might influence the relation between stress-induced PFC activity and the systemic response to mental stress," they explain. Another important factor missing from this research is adrenal steroid hormones. These reflect the activity of the HPA axis and so it remains unclear what is the relationships between among stress-induced PFC activity, skin condition, and adrenal steroid hormones. There are also limitations to NIR spectroscopy itself in such studies. NIRS measures changes in haemoglobin oxygenation within the illuminated area, however, this includes both intracranial and extracranial tissues and so changes in NIRS parameters could reflect changes in blood flow to the scalp rather than changes in the brain. "We observed minimal changes in the skin blood flow during the task in a preliminary experiment," the researchers add, which suggests that their results do indeed pertain to blood flow changes in the PFC and not the scalp. Related links:
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