The secretion of fluid by the sweat glands: perspiration. Sweating occurs naturally when the sweat glands (sudoriferous glands) situated in the top layers of the skin discharge sweat through tiny openings in the surface. Sweating is necessary to remove certain waste products from the body, including urea; it is also essential in the regulation of body temperature, because as sweat dries, it has a cooling effect. Sweat is a transparent, colorless, acidic fluid with a characteristic odor caused by waste products.