Sweating (also called perspiration or sometimes transpiration) is the loss of a watery fluid, consisting mainly of sodium chloride and urea in solution, that is secreted by the sweat glands in the skin of mammals. Sweat also consist of the chemicals or odorants 2-methylphenol and 4-methyphenol.

In humans, sweating is primarily a means of temperature regulation. Evaporation of sweat from the skin surface has a cooling effect due to the latent heat of evaporation of water. 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 cold. 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

In humans, there are two kinds of sweat glands which differ greatly in both the composition of the sweat and its purpose:

Eccrine sweat glands, which are distributed over the entire body surface. These produce sweat that is composed chiefly of water with various salts. These glands are used for body temperature regulation.

Eccrine 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 sweat glands are controlled by sympathetic cholinergic nerves which are controlled by a centre in the hypothalamus. The hypothalamus senses core temperature directly, and also has input from temperature receptors in the skin and modifies the sweat output, along with other thermoregulatory processes.

Human eccrine 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 concentration of sodium varies from 35 to 65 mmol/l and is lower in people acclimatised to a hot environment. The sweat of other species generally differ in composition.

Apocrine sweat glands, that produce sweat that contains fatty materials. These glands are mainly present in the armpits and around the genital area and their activity is the main cause of sweat odour, due to the bacteria that break down the organic compounds in the sweat from these glands. Emotional stress increases the production of sweat from the apocrine glands, or more precisely: the sweat already present in the tubule is squeezed out. Apocrine sweat glands essentially serve as scent glands.

In some areas of the body these sweat glands are modified to produce wholly different secretions, however, including the wax of the outer ear. Others are greatly enlarged and modified to produce milk.

See also

• bromhidrosis
• diaphoresis
• hyperhidrosis
• anhidrosis

References

• Ferner S, Koszmagk R, Lehmann A, Heilmann W., Z Erkr Atmungsorgane. 1990;175(2):70-5. 'Reference values of Na(+) and Cl(-) concentrations in adult sweat'

External link

• Sweating and body odor on cnn.com (http://www.cnn.com/HEALTH/library/DS/00305.html)