Sweat, or perspiration, is a liquid made by the skin when the body is hot. Sweat is made in sweat glands under the surface of the skin. It comes out of tiny holes in the skin called pores. Sweat is mostly water, but it also contains some salts.
The body makes sweat to cool itself down. It is part of the body's thermoregulation. The sweat takes the heat from the body when it evaporates (turns to gas).