Evaluation of Hair Cycle and Epidermal Turnover.

The proliferation, differentiation and termination of cells are periodically repeated in the epidermis. Hair growth and shedding are also repeated in cycles. We have developed an evaluation method with electronic equipment to examine the details of the hair cycle and epidermal turnover. In this review, we describe 1) the differences in the length of the hair cycles between terminal hair and vellus hair, 2) the differences in the hair growth parameters between patients with androgenic alopecia and age-matched controls, and 3) the variation in the turnover rate in the stratum corneum among small areas on the skin surface. We also outlined various noninvasive methods to evaluate the dynamic aspects of the epidermis and hair.