Eccrine glands are one of the three kinds of sweat glands present in the skin, along with apocrine and sebaceous glands. Human skin contains between two and three million of these glands, mostly on the palms of the hands, the soles of the feet, and the armpits. Eccrine glands are seen as being a uniquely human structure in that they occur among other primates with only half the frequency as among humans. In non-primate animals, they are either confined to the pads of the feet and lip margins, or are entirely absent.
The evolutionary purpose of eccrine sweat glands among humans is somewhat controversial. Sweating is one of the least effective of the thermoregulation mechanisms among mammals. In extreme environments, it could even lead to severe dehydration and death. For that reason, it is believed by some that thermoregulation is actually a secondary purpose of sweating, and that some other function, such as the removal of waste salts, accounts for the proliferation of eccrine glands in humans.
While apocrine and sebaceous glands produce oily, waxy secretions that are associated with body oils and odors, the sweat from eccrine glands, being mostly water, generally does not cause unpleasant odors. These glands are also distinct in that while sebaceous and apocrine glands are usually attached to a hair follicle, eccrine glands are always open on the surface of the skin.
Eccrine glands are controlled by the sympathetic nervous system. When the nervous system detects a rise in temperature either from external heat or fever, the sweat glands are stimulated to cover the skin with a thin film of water, the evaporation of which dissipates heat and cools the body. These glands are noted as being highly adaptable to a variety of environments, becoming more active in hotter climates and less active in cold regions. Emotional stressors can also stimulate eccrine glands, in which case sweating is confined mostly to the palms of the hands and soles of the feet, as opposed to the more global activity associated with thermoregulation.
Occasionally, either due to genetics or an underlying medical disorder, sweat glands become overactive and sweating becomes profuse to the point of being bothersome. Treatment options for this condition – known as hyperhidrosis – range from the very mild, such as prescription antiperspirants, to more invasive procedures such as Botox™ injections. It even could include surgical interruption of the nerve impulses that govern the sweat glands.