Urea, ammonia, and uric acid are waste products of protein metabolism. These waste products are toxic to the body. Sweat glands are coiled, tubular glands. Their ducts open at the skin's surface, similar to the opening of a hair follicle. Once secreted onto the surface of the skin, the sweat evaporates, cooling the surface.
Sweat glands receive messages from the nervous system.
These messages can alter the production of sweat. For example, sweating can be increased by being nervous or by eating spicy foods. A second type of sweat is present in the armpit, nipple, and anal regions. These glands open into a hair follicle, rather than directly onto the skin's surface. These glands produce a thick secretion that is odorless.