Structural and Biochemical Changes in Aging Skin and Their Impact on Skin Permeability Barrier

Publisher Summary Skin transformations are the most perceptible signs of aging. The multifaceted functions of the skin include acting as an entry barrier to compounds, regulating body temperature and fluid and electrolyte balance, and providing receptors for sensations such as touch, pain, and pressure. This chapter presents a synopsis of systematic and detailed studies on this topic. As skin ages, it undergoes certain morphological and functional changes, which lead to altered drug permeability, increased susceptibility to irritant contact dermatitis, and in addition possibly severe xerosis. From the published literature, it seems that the thickness of the stratum corneum does not change significantly with age, but there is an increase in the surface area of the corneocytes. Other major changes include reduced elasticity of the epidermis, a decrease in the number of sweat glands and an increased loss of collagen and elastin. There are a number of smaller variations occurring structurally and biochemically with age such as the reduction in skin lipids and a reduction in cell turnover. The complex nature and high number of changes occurring simultaneously as well as the experimentally introduced variations due to the use of subjects of different races, genders, ethnicity, and ages make it difficult to draw conclusive correlations between such changes and alterations in permeation of drugs through aged skin.