ABSTRACT
Optimal hydration is one of the key factors for effective functioning of the stratum corneum (SC) to maintain flexibility and to facilitate the enzymatic reactions that drive SC maturation (1). Decreased water content impairs the natural desquamation process and leads to the formation of dry scaly skin (2). Moisturizing products are typically used to relieve the symptoms of dry skin and the efficacy of these products is determined in part by evaluating their ability to improve skin hydration. The state of skin hydration has been often assessed through instrumental methods that depend on the correlation of skin hydration with the electrical conductance and capacitance responses of the skin (3-5). These electrical methods have been used previously in differentiating products with large differences in hydration benefits, for example, between harsh soap and syndet cleansing bars and between moisturizers and moisturizing cleansing liquids. While it is widely accepted that these electrical measures correlate with skin hydration, they are both indirect, contact methods and the relationship between the electrical response and the skin hydration level is not straightforward. Their reliability may be an issue, as well, particularly if ingredients deposited on the skin from skin care products have a significant contribution (positive or negative) to the electrical property measured (6). Additionally, it is evident that substances or treatments that interact with the keratin-water network of the SC can change the electrical properties of skin without actually altering water content (5).
