The average human body is covered with about 20 square feet or 2 square meters of skin. Weighing almost 6 pounds (2.7 kilograms), the skin is composed of two main layers: the epidermis (outer layer) and the dermis (inner layer). The epidermis layer is replaced continually as new cells, produced in the stratum basale, mature and are pushed to the surface by the newer cells beneath; the entire epidermis is replaced in about 27 days. The dermis, the lower layer, contains nerve endings, sweat glands, hair follicles, and blood vessels. The upper portion of the dermis has small fingerlike projections, called "papillae," which extend into the upper layer. The capillaries in these papillae deliver oxygen and nutrients to the epidermis cells and also function in temperature regulation. The patterns of ridges and grooves visible on the skin of the soles, palms, and fingertips are formed from the tops of the dermal papillae. (The Handy Science Answer Book, compiled by the Science and Technology department of the Carnegie Library of Pittsburgh; Encarta Encyclopedia)
