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Overview of the Skin

by Robert J. MacNeal, MD

The skin is the body’s largest organ. It serves many important functions (see Structure and Function of the Skin), including regulating body temperature, maintaining water and electrolyte balance, and sensing painful and pleasant stimuli. The skin keeps vital chemicals and nutrients in the body while providing a barrier against dangerous substances from entering the body and provides a shield from the harmful effects of ultraviolet radiation emitted by the sun. In addition, skin color, texture, and folds (see Descriptions of Skin Marks, Growths, and Color Changes) help mark people as individuals. Anything that interferes with skin function or causes changes in appearance (see Effects of Aging on the Skin) can have important consequences for physical and mental health.

Many problems that appear on the skin are limited to the skin. Sometimes, however, the skin provides clues to a disorder that affects the entire body. Consequently, doctors often must consider many possible diseases when evaluating skin problems. They may need to order blood tests or other laboratory tests to look for an internal disease in people who come to them with a skin problem (see Diagnosis of Skin Disorders).