Kinetics of epidermis and adnexa following vitamin A acid in the human.

The effects of topically applied vitamin A acid and benzoyl peroxide were investigated. Short-term (a few days) and long-term (up to 800 days) treatment was analyzed histologically and autoradiographically. Labelled and unlabelled biopsies at various time intervals were taken from face, back, and acne lesions. Kinetics were followed with 3H-TdR and 3H-histidine. All keratinizing epithelia of epidermis and adnexa are stimulated by vitamin A acid. Labelling is high (up to 20-70% L.I) and occurs within a few days. Follicles and comedones can also be stimulated, but respond less and much later than epidermis. Transit time is shortened to 3-4 days. Lose, incoherent horny cells are produced, explaining the therapeutic benefits of vitamin A acid in acne. Benzoyl peroxide is less effective in stimulating epidermopoieses in epidermis, follicles, and comedones. This autoradiographic analysis parallels therapeutic results with these two exfoliants.