As one of the major soluble substances of the stratum corneum(skin-building layer), urea has a growing importance in dermatological therapy and cosmetics. Diseases such as atopic dermatitis or clinical dry skin are marked by deficiency of urea. Urea is of significance for the hydration of the stratum corneum because it is a humectant that draws moisture into the skin.

Studies have been done where the amount of urea on extracts from the stratum corneum of normal skin is compared to that of skin after cleansing and after prolonged topical application of urea emulsions. It was found that skin cleansing led to a dramatic decrease in the amount of urea found in the stratum corneum. On the other hand, when skin care formulations containing urea were applied, a significant increase of the amount of urea in the stratum corneum was measured.

As a conclusion, the urea content in the stratum corneum varies. After skin cleansing, its status is reduced, whereas, after a prolonged application of urea-containing emulsions, its level is increased. Thus regular use of urea-containing emulsions will increase the levels of urea in the skin and keep the skin hydrated and moisturized.