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Issue
21 — October 1999 |
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Title |
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Reference |
| Newsletter |
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Urea
— Its Role in Cosmetics |
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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.
Literature
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 cosmetic and dermatological ingredient,
Skin Care Forum No. 11 (1995) 7-9
