Cell Replacement in the Human Stratum Corneum in Old Age

SUMMARY. Staining of the human stratum corneum in vivo with fluorescent tetrachlorsalicylanilide has been used to measure the transit time of horny cells in the normal forearm skin of aged people. Stratum corneum thickness was estimated by counting the horny cell layers in biopsy specimens of epidermis, visualized by hydration in alkali. From the two parameters thus obtained, stratum corneum replacement rates were: calculated. In 6 aged men, transit times varied between 20 and 36 (mean 26) days, and replacement rates between 30 and 47 (mean 34) hr. per cell layer. These data suggest reduced epidermal mitotic activity compared with that of young men. In 5 aged women, transit times varied between 17 and 26 (mean 20) days and replacement rates between 16 and 31 (mean 24) hr. per cell layer. This faster replacement in old women compared with old men is not much slower than that observed in young adults.