ABSTRACT
As a physiological regulator, the skin plays a major role in the general metabolism of water in the body. Therefore the moisture level of the stratum corneum is crucial to keep the cutaneous surface supple and healthy. Lipids can be found in the cellular membrane and the interstices; they change dramatically in quality and quantity as soon as epidermal cells leave the basal layer to turn gradually into desquamating cells. Qualitative and quantitative changes in the composition of both the surface lipidic film and natural moisturizing factors (NMFs) components were shown in many skin diseases. These changes bring about a high cutaneous dehydration, often associated with desquamation and chapping. In order to retain and bind water at the skin surface, hygroscopic substances are used. Examples are the active principles of NMF and particularly the sodium salt of 2-pyrrolidone-5-carboxylic acid—a physiological moisturizer found in various organs, organic fluids, and particularly the epidermis, including the stratum corneum.
