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Close view of the skin on a human hand.

Skin is the outside covering of mammals and some other animals. It has many purposes. First of all, it is a defense against the entry of pathogens such as bacteria and parasites. Second, it regulates (keeps in control) the body's temperature. It allows evaporation from its surface, and adjusts it. It is a physical defense, very strong in some animals, but rather weak in humans. The skin and hair on mammals has several purposes. In addition to temperature regulation and defense, some hair is used for signaling.