Sweat helps keep us cool in hot weather or when exerting ourselves and is hence an important part of thermoregulation, the maintenance of a uniform body temperature. By moistening our skin, sweat cools us as it evaporates. It also aids in excretion, or the removal of waste products from the body, and helps protect the skin from such environmental hazards as bacteria and chemicals.

Sweat consists primarily of water, but always has about 0.2 to 1% solute made up of minerals, lactate, and urea. In addition to being triggered by a rise in temperature, sweat can also be caused by nausea and stress. Cooling the body typically reduces sweating.

Sweat glands in the skin are controlled by the hypothalamus in the brain, part of the autonomic nervous system. Temperature receptors in the skin affect the body's hypothalamic, or core, temperature, which in turn sends signals to the hypothalamus. Heated skin lowers the hypothalamic set point or threshold at which sweating begins. When this set point is reached, the hypothalamus sends signals to activate the sweat glands.

Sweat glands are coiled, tubular structures in the epidermis, or skin. Each sweat gland has myoepithelial cells that contract when activated. This motion squeezes the glands, excreting sweat directly onto the surface of the skin.

Human skin contains two types of sweat glands, merocrine and apocrine. Merocrine sweat glands are more numerous and widespread and shallower than apocrine sweat glands. They are located all over the body, with the highest concentrations on the palms and soles of the feet. Merocrine sweat glands are responsible for most of what we call sweat or perspiration.

Apocrine sweat glands are located in the armpits, groin, and around the nipples. They secrete a more viscous, cloudy product and become active at puberty. The presence of bacteria in these glands sometimes causes a noticeable scent. It has been hypothesized that these sweat glands secrete pheromones, which can potentially communicate signals to others by affecting their hormonal levels.