A simple method for estimating the turnover time of the human stratum corneum is described. The horny layer is impregnated with a fluorescent dye and the site followed until the fluorescence disappears.
The renewal time for the stratum corneum of the back was found to be about two weeks, for the back of the hand three weeks, and for the forehead one week. The increased time on the back of the hand is probably related to the increased thickness of the horny layer at this site. The reduced forehead time is not related to thickness and may reflect a real increase in epidermal turnover rate at this site.
Baker H, Kligman AM. Technique for Estimating Turnover Time of Human Stratum Corneum. Arch Dermatol. 1967;95(4):408-411. doi:10.1001/archderm.1967.01600340068016