S13-4. Changes of stress responses induced by fragrance: A NIRS study

Fragrances have long been known to influence stress-induced psychosomatic disorders; however, the neurophysiological mechanism remains unclear. In the present study, 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 NIRS, we measured hemoglobin concentration changes in the bilateral PFC during a mental arithmetic task in normal adults, and evaluated asymmetry of the PFC activity in terms of the laterality index (Li). 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. We selected the subjects who exhibited high levels of sebum secretion and right-dominant PFC activity for the study on the fragrance effect. Administration of fragrance for four weeks significantly reduced the level of sebum ( p  = 0.02) in the fragrance group. In addition, the dominant side of the stress-induced PFC activity changed from the right to left side. These results suggest that administration of fragrance reduced the level of sebum secretion by modulating the stress-induced PFC activity.