The role of urea in skin care

Description

Urea is the diamide of carbonic acid with the chemical formula H2NCONH2. It is a colorless, crystalline substance that melts at 132.7° C (271° F) and decomposes before boiling. This compound has important uses as a fertilizer, feed supplement, and a starting material for manufacturing plastics and drugs[1]. Both urea and urine are different. In humans, urea is a nitrogen-containing waste substance that the kidneys clear from the blood and excrete into the urine. Human urine consists of water, urea, inorganic salts, creatinine, ammonia, and pigmented products.

Effects on the skin

Urea is a naturally occurring humectant agent that is part of the water-soluble fraction of the stratum corneum. It can both retard and promote penetration into the skin. Enhancement of skin barrier function has been frequently reported, and thus, urea is widely used to improve skin dryness. In many skin diseases characterized by dryness, such as atopic and hand eczema, urea can delay relapses in these highly chronic conditions. With this in mind, urea has been used as a well-established ingredient in various topical applications for skin care and skin diseases.

High concentrations of urea (20%-40%) dissolve atrophic nails or destroyed ones in tinea unguium. In hyperkeratotic feet, urea can improve the situation at concentrations of 10%-40%. Furthermore, urea (10%) can reduce the thickness of the stratum corneum by reducing the number of stratum corneum cell layers. Urea also improves the skin's water-holding capacity, which becomes clinically useful in ichthyotic skin. In psoriasis, urea (10%) can reduce plaque thickness but does not show effects on erythema; it is not directly anti-inflammatory in this condition. Urea also improves the skin's water-holding capacity, which becomes clinically useful in ichthyotic skin. In psoriasis, urea (10%) can reduce plaque thickness but does not show effects on erythema; thus, it is not directly anti-inflammatory in this condition[2].

Physical properties of urea, such as detachment of nails, are because of its ability to unfold proteins, thus destroying them. Urea can also replace water and increase the resistance of the stratum corneum against osmotic stress. Thymidine incorporation into DNA was observed after short-term contact with a saturated urea solution. More recently, effects of urea beyond the physical ability to be part of the natural moisturizing factor have been reported, throwing light on new aspects of action. It seems that urea can stimulate epidermal differentiation and lipid synthesis and induce the synthesis of antimicrobial peptides in the epidermis as part of the skin's immune system[3]. Various findings support the ability of urea to take effect on gene transcription: human keratinocytes react on stimulation with physiological doses of urea in the millimolar range by expression of transglutaminase, involucrin, filaggrin, and loricrin.

References

[1] Wei Xu, Prof. Shanwen Tao, Prof. Zucheng Wu. “Urea-Based Fuel Cells and Electrocatalysts for Urea Oxidation.” Energy technology 4 11 (2016): 1329–1337.

[2] Dirschka, Thomas. “Mode of action of urea.” International Journal of Clinical Practice 74 S187 (2020).

[3] I Hagemann, E Proksch. “Topical treatment by urea reduces epidermal hyperproliferation and induces differentiation in psoriasis.” Acta dermato-venereologica 76 5 (1996): 353–6.