In its most widely appreciated context, the stratum corneum (SC) exhibits an important barrier function extending to protection from ultraviolet light, oxidants, micro-organisms, and toxic xenobiotics. It also protects from loss of water and electrolytes from the body. The SC can also be viewed as a highly specialized structure showing perpetual renewal keeping ideally a steady state in its structure and thickness. It is structurally and biochemically diverse. It possesses a limited form of metabolic activity. It also acts as a unique sophisticated biosensor that signals the underlying epidermis to respond to external stresses.1,2

Corneocytes are about 1 µm thick and have a mean area of approximately 1000 µm2. However, the surface area is dependent upon age, anatomical location, and conditions that influence epidermal proliferation such as chemical irritation and UV irradiation.3 Corneocyte size increases with age. This is sometimes assumed to be related to the increased transit time within the SC. On most body sites, the SC consists typically of 12 to 16 layers of flattened corneocytes.