[Promoting penetration of locally applied substances by urea]

These studies indicate that urea alters the physical and chemical properties of keratin so that permeation of monosubstances in urea-altered keratin is increased. The permeation kinetics of keratin can be influenced by splitting and/or altering the surface structure of keratin, which enhances the permeation of steroids, dithranol, and other substances. The regulation of permeation kinetics in the horny layer also applies to urea. The permeation of urea in and through the horny layer can lead to an alteration in the binding capacity within this layer (reservoir capacity). Thus, the penetration of substances such as oxiconazol through the horny layer can be decreased and their retention time increased. Nevertheless, urea is not always the stimulator of permeation processes.