Urea and Liquid Crystal: The Better Option for Skin Hydration

The skin's main function is to be a physical barrier, which prevents transepidermal water loss (TEWL) and protects the body from the external environment. Changes in the structure of the stratum corneum impair the barrier function and favor the appearance of several skin diseases, including xerosis, atopic dermatitis and psoriasis. Skin health is preserved by the presence of structurally organized intercellular lipids in the stratum corneum, which are responsible for cell adhesion, preserving hydration and reducing TEWL. Changes in the lipid-protein structure or changes in the composition of the Natural Moisturizing Factor (NMF) can cause reduced hydration of the stratum corneum, resulting in dry skin with sensory symptoms such as opacity, roughness, scaling, stiffness, fissures, itching and even bleeding. Skin care cosmetics having the presence of liquid crystals resembling structurally the intercellular lipids in the stratum corneum and can beneficially affect the skin when applied topically by stimulating the skin’s natural regenerative functions of stratum corneum. We have developed an O/W emulsion for skin care whose structure observed under polarization microscopy is similar to that of the lipid distribution of the stratum corneum: the emulsion presents a lamellar crystalline phase. The formulation was composed by a blend of surfactant [lanolin derivatives plus 2EO fatty alcohol (50:50)] + liquid paraffin+ purified water. Urea was employed as hydration agent. The occlusive power of O/W was determined in vitro onto gelatin support cells (noninvasive method) and in vivo method- skin hydration, skin oiliness and skin pH evaluation. The developed formulation significantly increased the occlusive power of emulsion. Skin hydration was studied by using an in vitro non-invasive methodology and it was found that the presence of liquid crystal in the emulsion increases the skin hydration level. This was attributed to the fact that it formed the same self-organizing structure as natural stratum corneum lipids.