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The skin has three layers—the epidermis, dermis, and fat layer (also called the subcutaneous layer). Each layer performs specific tasks. | | | | Getting Under the Skin | | The skin has three layers. Beneath the surface of the skin are nerves, nerve endings, glands, hair follicles, and blood vessels. | |
Epidermis: The epidermis is the relatively thin, tough, outer layer of the skin. Most of the cells in the epidermis are keratinocytes. They originate from cells in the deepest layer of the epidermis called the basal layer. New keratinocytes slowly migrate up toward the surface of the epidermis. Once the keratinocytes reach the skin surface, they are gradually shed and are replaced by younger cells pushed up from below.The outermost portion of the epidermis, known as the stratum corneum, is relatively waterproof and, when undamaged, prevents most bacteria, viruses, and other foreign substances from entering the body. The epidermis (along with other layers of the skin) also protects the internal organs, muscles, nerves, and blood vessels against trauma. In certain areas of the body that require greater protection (such as the palms of the hands and the soles of the feet), the outer keratin layer of the epidermis (stratum corneum) is much thicker.Scattered throughout the basal layer of the epidermis are cells called melanocytes, which produce the pigment melanin, one of the main contributors to skin color. Melanin's primary function, however, is to filter out ultraviolet radiation from sunlight (see Sunlight and Skin Damage: Overview of Sunlight and Skin Damage), which can damage DNA, resulting in numerous harmful effects, including skin cancer. the epidermis also contains Langerhans' cells, which are part of the skin's immune system. Although these cells help detect foreign substances and defend the body against infection, they also play a role in the development of skin allergies.Dermis: The dermis, the skin's next layer, is a thick layer of fibrous