Effects of fragrance administration on stress-induced prefrontal cortex activity and sebum secretion in the facial skin.

Although fragrances have long been known to influence stress-induced psychosomatic disorders, the neurophysiological mechanism remains unclear. We evaluated the effect of fragrance on the relation between the level of sebum secretion in the facial skin and the stress-induced prefrontal cortex (PFC) activity, which regulates the activity of the hypothalamic-pituitary-adrenal axis. Employing near infrared spectroscopy, we measured hemoglobin concentration changes in the bilateral PFC during a mental arithmetic task in normal adults (n=31), and evaluated asymmetry of the PFC activity in terms of the laterality index (i.e., [(right-left)/(right+left)]) of oxyhemoglobin concentration changes (LI-oxyHb). We measured the level of sebum secretion in the facial skin before the task performance. There was a significant positive correlation between the LI-oxyHb and the level of sebum secretion (r=+0.44, p=0.01). We selected the subjects who exhibited high levels of sebum secretion and right-dominant PFC activity for the study on the fragrance effect (n=12). Administration of fragrance for four weeks significantly reduced the level of sebum (p=0.02) in the fragrance group (n=6). In addition, the LI-oxyHb decreased significantly from 0.11+/-0.07 to -0.10+/-0.18 (p=0.01), indicating that the dominant side of the stress-induced PFC activity changed from the right to left side. In contrast, neither LI-oxyHb nor the levels of sebum secretion changed significantly in the control group (n=6). These results suggest that administration of fragrance reduced the level of sebum secretion by modulating the stress-induced PFC activity. The PFC may be involved in the neurophysiological mechanism of fragrance effects on systemic response to mental stress.