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| Newsletter | Urea — Its Role in Cosmetics |
As one of the major soluble substances of the stratum corneum, urea has a growing importance in dermatological therapy and cosmetics. Diseases such as atopic dermatitis or clinical dry skin are marked by a deficiency of urea. Urea is of significance for the hydration of the stratum corneum. Normal skin contains approximately one percent urea. Furthermore, urea has keratolytic and pruritus-easing properties and may be incorporated as an active ingredient in moisturizers due to its humectant properties.
A rapid, safe and non-invasive method to determine the water-soluble urea content in the stratum corneum is allowed by a rapid enzymatic assay using water as the only extraction solvent. The extraction of water-soluble urea from the stratum corneum was performed with the aid of a plastic cylinder fixed on the skin. The urea distribution was determined on the volar forearms of volunteers. This method may be used routinely on human volunteers when testing skin formulations and cleansing products and allows the simultaneous determination of up to 20 skin extracts.
The amount of urea in extracts from the 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 was measured.
Skin cleansing with sodium lauryl sulphate solution (SDS, 4 percent), a standard cleansing product and water as a control led to a dramatic decrease in the amount of extractable urea from the stratum corneum (see Figure). If a cleansing product was supplemented with 10 percent urea, a measurable positive effect on extractable urea was achieved.
If skin care formulations containing urea were applied, a significant increase of the amount of urea that could be solubilized from the stratum corneum was measured. The skin care formulations were a special cream without urea and a special cream with 5 percent urea. If skin was treated with the special cream containing 5 percent urea, there was a significant increase in the urea content of the stratum corneum compared to an untreated area and a treatment with the special preparation without urea. A lasting effect for at least 24 hours after final application of the urea-containing cream was observed.
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. In pathological skin diseases, these results may be of importance to compensate for urea deficiencies. In dry skin, a lack of water-retaining substances may be compensated by urea-containing cosmetics.
Reference
Häntschel, D.; Sauermann, G.; Steinhart, H.; Hoppe, U.; Ennen, J.; Urea analysis of extracts from stratum corneum and the role of urea-supplemented cosmetics, J. Cosmet. Sci., 49 (1998) 155-163
Bohnsack, K.; Urea - An effective and safe Ccosmetic and dermatological ingredient, Skin Care Forum No. 11 (1995) 7-9
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