Urea analysis of extracts from stratum corneum and the role of urea-supplemented cosmetics

This investigation was undertaken to quantify the amount of urea in extracts from stratum corneum of normal skin in comparison to extracts from skin after cleansing, or from skin after a prolonged topical application of urea-supplemented emulsions. We measured a dramatic decrease in the amount of extractable urea from stratum corneum after skin cleansing. This loss of urea can be partially compensated by a cleansing formula supplemented with urea. On the other hand, a skin care emulsion with urea supplementation increases significantly the amount of urea that can be solubilized from stratum corneum. From these results we conclude that the urea content of stratum corneum varies in a wide range, limited at the lower end by a reduced status that can be observed when skin cleansing had been performed, and at the higher end by an increased level that can be obtained after prolonged application of urea-containing emulsions. These findings might have important implications for therapeutic compensation of urea deficiency in pathological skin diseases and also for cosmetic compensation for a lack of water-retaining substances in dry skin.