Assessment of moisturizers and barrier function restoration using dynamic methods

Dynamic methods, such as the mathematical modelling of the transepidermal water loss curves that result from a plastic occlusion stress test (POST), enable the complete characterization of the dynamic water balance established between the deep and the superficial skin structures. Previous studies have indicated that this methodology was able to detect impaired barrier function and differentiate normal and dry skin. The objective of the present study is to apply the discriminative capacity of the model to the efficacy testing of moisturizing products. A moisturizing cream containing urea was applied for 2 weeks to the lower leg of volunteers with dry skin. After this period, a POST was performed in the treated and control untreated site and a mathematical model was adjusted to the resulting desorption curves. Results indicate that, after treatment of the skin with the cream for 2 weeks, statistically different kinetic parameters are obtained in the treated site, which suggests an improvement in the water dynamic balance and skin barrier. The data generated by this study was compared with that obtained in a similar investigation that was performed a year earlier. Analysis of the dispersion of results indicates that the method has good reproducibility. These findings confirm that the method has enough sensitivity to assess in vivo the effect of moisturizers on human skin, and also that this evaluation can be performed in a shorter period than that required by the regression method. This methodology can also be considered more informative, because the analysis of the different parameters obtained by the model is indicative of the mechanism of action of the product applied to the skin