Human skin equivalents are an excellent tool to study the effect of moisturizers on the water distribution in the stratum corneum

In this study, the mode of action of moisturizers on the level of water in the stratum corneum was studied using cryo-scanning electron microscopy. As model for dry skin, we used human skin equivalents (HSEs) generated at 93% or 60% relative humidity (RH). During the generation of the HSEs, the moisturizers were applied during a period of maximal 2 weeks. In HSEs generated under normal culture conditions (93% RH), application of 10% glycerol or 5% urea formulations resulted in increased water levels. Whereas the 5% urea formulations resulted mainly in the formation of intercellular water domains, after 10% glycerol both swelling of corneocytes and formation of intercellular water domains were noticed. A reduction in RH to 60% during treatment reduced the stratum corneum water levels drastically. Treatment with the non-occlusive lipophilic moisturizer isopropyl isostearate resulted in increased water level in the central part of the stratum corneum compared with the untreated control. Our results show that HSEs can be used as a model to study the water distribution.