bond pulls the skin back to its natural shape. The thickness of the stratum corneum varies throughout the body. In the palms of the hands and the soles of the feet (sometimes knees, elbows, knuckles,) this layer is stabilized and built by the stratum lucidum (clear phase) which allows the cells to concentrate keratin and toughen them before they rise into a typically thicker, more cohesive SC. The mechanical stress of heavy structural strain causes this SL phase in these regions which require additional protection in order to grasp objects, resist abrasion or impact, and avoid injury. In general, the stratum corneum contains 15 to 20 layers of corneocytes. The stratum corneum has a thickness between 10 and 40 μm. In reptiles, the stratum corneum is permanent, and is replaced only during times of rapid growth, in a process called ecdysis or moulting. This is conferred by the presence of beta-keratin, which provides a much more rigid skin layer. In the human forearm, about 1300 cells per cm2 per hour are shed. Stratum corneum protects the internal structures of the body from external injury and bacterial invasion. Skin disease An inability to correctly maintain the skin barrier function due to the dysregulation of epidermal components can lead to skin disorders. For example, a failure to modulate the activity of kallikreins via the disruption of the protease inhibitor LEKTI causes the debilitating disorder Netherton syndrome. Hyperkeratosis is an increased thickness of the stratum corneum, and is an unspecific finding, seen in many skin conditions. See also Epidermis (skin) Stratum granulosum Stratum spinosum Kallikrein-5 Hexastix References External links - "Integument: thick skin" Skin anatomy Epithelial cells de:Epidermis (Wirbeltiere)#Stratum corneum