Stratum corneum dynamic function measurements after moisturizer or irritant application.

Two simple tests were conducted which allowed the quantification of parameters that characterize the stratum corneum (SC) dynamic functions in vivo under physiological conditions after moisturizer applications for 1 h and after irritation with different concentrations of sodium lauryl sulphate (SLS; 0.5-4%) applied under occlusion for 15 min or 24 h. Both tests, the sorption-desorption test (SDT) and the moisture accumulation test (MAT), were performed with a Nova Dermal Phase Meter 9003. The following parameters were quantified: prehydration state (SDT, MAT), hygroscopicity, water-holding capacity (SDT), water accumulation velocity and water accumulation (MAT). These procedures allowed the demonstration of the water-holding effect of urea contained in moisturizers. Differences between the long and the short application time of SLS were characterized by differences in SC dynamic functions while the hydration state was not changed. An effect on transepidermal water loss (TEWL) was noted only after the long application time, although the MAT clearly showed dynamic parameters to be changed after 15 min of treatment. These tests were simple in practice and allowed the demonstration of functional modifications of the SC while other parameters remained unchanged. They gave insight into possible action mechanisms of urea and SLS in the SC.