skin
n. the external covering of the body, consisting of an outer layer (epidermis) and a deeper layer (dermis) resting on a layer of fatty subcutaneous tissue. The skin is well supplied with nerves and blood vessels and forms an effective yet sensitive barrier that prevents the entry of foreign substances and pathogens into the body. It defends against injury to underlying tissues, reduces water loss from the body, and forms part of the body’s temperature-regulation mechanism through the evaporation of sweat secreted from sweat glands. Human skin typically has only a sparse covering of hair, except on the head and genital regions, and the hair has minimal value as insulation, although it is often highly significant in social terms. In humans, insulation is provided mainly by the subcutaneous adipose tissue. The root of each hair arises from a hair follicle, into which the ducts of sebaceous glands discharge sebum, an oily secretion that
lubricates and waterproofs the skin surface. Various types of sensory nerve endings provide the skin with touch and pressure sensitivity, as well as sensations of pain and temperature (see cutaneous receptor).