Humectants (see Table 3 ) are able to attract water from two sources: they enhance water absorption from the dermis into the epidermis, and in humid conditions they also help the SC to absorb water from the external environment. Many humectants also have emollient properties.
The most effective humectant is the trihydroxylated molecule, glycerol. Immature corneocytes are fragile but mature into more resilient and protective cells as they migrate through the SC.[7,17] Glycerol hastens the maturity of corneocytes through the activation of residual transglutaminase activity in the SC. Also, by facilitating the digestion of desmosomes and subsequently enhancing desquamation, glycerol reduces the scaling associated with xerosis.
Found in the NMF, pyrrolidine carboxylic acid hydrates the skin, and has been shown to improve xerosis.
Alpha hydroxy acids (e.g., lactate) are effective agents for the treatment of dry skin; following treatment with lotions containing D-, L-lactic acid, the SC prevents xerosis more effectively. Lactic acid, particularly the L-isomer, stimulates ceramide biosynthesis leading to higher SC ceramide levels that result in a superior lipid barrier and more effective resistance against xerosis.
One major drawback of humectants is that some of them can increase TEWL by enhancing water absorption from the dermis into the epidermis where it can then be lost into the environment. For this reason, they are almost always combined with an occlusive agent. Occlusive and humectant ingredients work together to enhance epidermal hydration and barrier function.
Skin Therapy Letter. 2005;10(5):1-8. © 2005 SkinCareGuide.com
Cite this: Moisturizers: What They Are and a Practical Approach to Product Selection - Medscape - May 01, 2005.