Changes in stratum corneum thickness, water gradients and hydration by moisturizers

Abstract

As the outermost layer of skin, the stratum corneum (SC), plays the pivotal role in protecting our bodies. It is the first line of defense against the outside world, providing both mechanical and chemical protection and regulating the movement of water and other materials in and out, enabling the bodies' equilibrium to be maintained. Despite the relatively small dimensions of the SC over most of the body (its thickness is of the order of only 20 μm over a large portion of the body), it has a very complicated chemical and physical structure. Chemical concentrations and cellular structure change across its thickness, and these changes are responsible for the properties it possesses and for regulating the processes occurring within it. To better understand the role all of these components play within the SC, therefore, is not only necessary to ask 'how much is there?', but also 'where is it located?' and 'how is it distributed?' While a number of techniques have been developed previously to analyze concentration gradients within the SC, until recently no single technique has been able to quantitatively assess different chemical components as a function of depth, rapidly and in vivo. Furthermore, as the use of topical cosmetic products has become more popular and widespread, especially in the anti-aging market, the ability to accurately monitor ingredients which are capable of penetrating into the skin is now a necessity. Also, it is becoming more and more important to demonstrate how topically applied products can improve the skin in clinical tests; therefore, new methods to assess the skin in greater and greater detail are constantly being explored.