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Perspiration (or sweat) is a watery fluid, consisting mainly of sodium chloride and urea in solution, that is secreted by the sweat glands in the skin of mammals.

In humans, sweating is a means of excreting nitrogenous waste products, but it is also, and more importantly, a means of temperature regulation. Evaporation of sweat from the skin surface has a cooling effect. Hence, in hot weather, or when the individual feels hot through exercise, more sweat is produced. Sweating is increased by nervousness and nausea and decreased by colds. Animals with few sweat glands, such as dogs, accomplish similar results by panting, evaporating water from the moist lining of the oral cavity and pharynx.

Sweat glands

Sweat glands are coiled tubular glands derived from the outer layer of skin but extending into the inner layer. They are distributed over almost the entire surface of the body in humans and many other species, but are lacking in some marine and fur-bearing species.

The secretion of sweat glands varies greatly. In humans, sweat is composed chiefly of water with various salts and organic compounds in solution. It contains minute amounts of fatty materials, urea, and other wastes. The sweat of other species normally differ in composition.

In some areas of the body the sweat glands are modified to produce wholly different secretions, however, including the wax of the outer ear. Some sweat glands, called apocrine glands, are modified into scent glands. Others are greatly enlarged and modified to produce milk. The ones used for temperature regulation are called eccrine glands.