ABSTRACT
Human perception is based on visualization of surfaces. Because we cannot look inside, we define objects through their interfaces. This, of course, holds true for human skin. The interface, which meets our eyes, is the stratum corneum, the dead outer layer of the epidermis, composed of flattened horny cells, which are constantly being shed. Still, the physical state of the stratum corneum often reflects changes that have occurred below in the viable tissue. For example, in the epidermis, either thickening (acanthosis) or thinning (atrophy) results in characteristic changes of the glyphic patterns. Inflammation is typically followed by scaling in patterns, which often enable us to diagnose the underlying disorder. Examples are endless, including dermal and epidermal pigmentation, respectively reflecting brown or blue coloration, and numerous forms of hyperkeratosis, follicular and nonfollicular, resulting in a rough, dry, cracked surface. Pathologic events in the dermis can cause soft or firm swellings of the surface. It is important to realize that clinical diagnosis frequently depends on how we perceive the surface. Knowledge about the stratum corneum in health and disease is thus crucial to dermatologic practitioners.
