[Significance of urea in external therapy]

Urea affects human skin by penetrating different skin layers. For this a strong vehicle dependence is evident. Therefore, considerable differences could be found in the duration and intensity of increased water-binding capacity after the application of different urea-containing emulsions. For therapy to increase the hydration and water-binding capacity in the horny layer of diseased skin, preparations with 10% urea are better suited than those containing 2% or 5% urea. By altering the functional structure of the horny layer and considerably increasing the drug's liberation from its ointment base, urea is one of the most effective penetration promoters. An increased penetration rate of some corticoids and dithranol from urea-containing ointment were demonstrated in human skin. The resulting penetration promotes two possible applications in topical therapy: an increased therapeutic effect for a given concentration of an active constituent or a given therapeutic effect with a reduced concentration of the active ingredient.