Disorders of keratinization
The complex but orderly processes of keratinization, and of cell cohesion and proliferation within the epidermis. As they proceed, the living keratinocytes of the deeper epidermis change into the dead corneocytes of the horny layer, where they are stuck together by inter-cellular lipids. They are then shed in such a way that the surface of the normal skin does not seem scaly to the naked eye. Shedding balances production, so that the thickness of the horny layer does not alter. However, if keratinization or cell cohesion is abnor-mal, the horny layer may become thick or the skin surface may become dry and scaly. Such changes can be localized or generalized.
During the last few years the molecular mechanisms underlying many of these have become clearer, including abnormal genetic coding for ker-atins, the enzymes involved in cell cohesion in the horny layer, and the molecules that are critical in the signalling pathway governing cell cohesion in the spinous layer.