TIME-DEPENDENT VARIATIONS OF THE SKIN BARRIER FUNCTION IN HUMANS - TRANSEPIDERMAL WATER-LOSS, STRATUM-CORNEUM HYDRATION, SKIN SURFACE PH, AND SKIN TEMPERATURE

Although circadian rhythms have been described for many human function s, there are minimal data on circadian rhythms related to skin physiol ogy, This study investigated the circadian rhythmicity of skin variabl es related to skin barrier function in humans, We measured transepider mal water loss, stratum corneum moisture, skin surface pH, and skin te mperature in 16 healthy volunteers (nine men and seven women, aged 23- 53 y), Subjects were sampled every 2 h in two sessions over a 24 h spa n, Twelve samples were obtained for each variable in the following sit es: forehead, forearm, upper back, and shin, We used cosinor analysis and ANOVA to validate observed differences, Time-dependent rhythms wer e detected in most skin variables except in stratum corneum hydration. We found a statistically significant circadian rhythmicity characteri zed by cosinor analysis in transepidermal water loss, skin surface pH, and skin temperature on the forearm, forehead, and shin, Peak-trough differences occurred in all locations, The values of the same variable s measured at different sites correlated positively, whereas the value s of the different variables did not. These results suggest that skin permeability is higher in the evening and night than in the morning, T hese data may be clinically relevant in several aspects applied to ski n physiology and topical drug application.