This report describes a new and simple technique to detect alterations in the rate of turnover in the epidermis without using any toxic chemical, such as a radiolabeled material. The method involves measuring the time course of the decrease of darkening of an ultraviolet A-irradiated site, compared with a non-irradiated control site. The turnover time of the persistent pigmentation on the inner side of the male forearm was 36.2 ± 6.2 days (age: 37.3 ± 11.3 years, mean ± standard deviation, n
= 6), which is in reasonable agreement with the epidermal turnover time previously measured by injecting [3
H] thymidine into human skin.
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