**5. Psychological factors that influence barrier function**

As described above, psychological stress impairs barrier homeostasis. To study the effects of stress on barrier homeostasis, we used three models of stress, i.e., immobilization, a crowded environment and a change of living place [Denda 1998][Denda 2000]. In each case, the barrier recovery rate was delayed after barrier disruption. The plasma corticosterone level was increased by each stress, and it was reduced by application of a sedative drug [Denda 2000]. The delay of barrier repair induced by psychological stress was also prevented by application of a sedative drug or glucocorticoid receptor antagonist [Denda 2000]. These results suggest that psychological stress stimulates increased production of glucocorticoids, which adversely affect skin barrier homeostasis. The effect of psychological stress on skin barrier homeostasis in humans has also been examined [Garg 2001]. Reduction of psychological stress might accelerate the skin barrier repair process. Several studies have demonstrated that certain odorants can reduce stress, acting like a sedative drug [Tsuchiya 1992]. These odorants prevented the delay in skin barrier recovery induced by psychological stress in both mice and humans [Denda 2000a][Denda 2000b]. These results suggest the feasibility of a new skin care strategy based on inhalation of specific odorants.

Physical and Chemical Factors that Improve Epidermal Permeability Barrier Homeostasis 209

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Fig. 5. Schematic illustration of the effect of mental stress on the endocrine system and on skin barrier function.
