Perspiration

Perspiration (also called sweating or sometimes transpiration) is the production and evaporation of a fluid, consisting primarily of water as well as a smaller amount of sodium chloride (the main constituent of "table salt"), that is excreted by the sweat glands in the skin of mammals. Sweat also contains the chemicals or odorants 2-methylphenol (o-cresol) and 4-methylphenol (p-cresol).

In humans, sweating is primarily a means of thermoregulation, although it has been proposed that components of male sweat can act as pheromonal cues ^[1]. 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's muscles heat up due to exertion, 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 temperature regulation results by panting, which evaporates water from the moist lining of the oral cavity and pharynx. Primates and horses have armpits that sweat similarly to those of humans.

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How sweat glands operate

Sweat glands are innervated by the sympathetic nervous system. The nerve terminal releases acetylcholine, which binds to M₃ receptors on the sweat gland and causes the secretion of sweat. Acetylcholine is partially degraded by Cholinesterase enzyme (AchE); thus anything which interferes with AchE activity causes excessive sweating.

There are two kinds of sweat glands, and they differ greatly in both the composition of the sweat and its purpose:

• Eccrine sweat glands are distributed over the entire body surface, but are particularly abundant on the palms of hands, soles of feet, and on the forehead. These produce sweat that is composed chiefly of water with various salts. These glands are used for body temperature regulation.
• Apocrine sweat glands 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 odor, due to the bacteria that break down the organic compounds in the sweat from these glands.

This means that sweating is extremely common in the hand area and the armpit area. Normally if you carry excess body weight, you tend to sweat quite excessively around the armpit area.

See also

• Diaphoresis
• Hyperhidrosis
• Anhidrosis
• Hyponatremia
• Hyperthermia
• Body odor
• Hidradenitis suppurativa
• Pheromones
• Sweat therapy

References

1. ^ Smelling a single component of male sweat alters levels of cortisol in women", C. Wyart et al., Journal of Neuroscience, February 7, 2006

Further reading

• 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'
• E. R. Nadel, R. W. Bullard, and J. A. Stolwijk, "Importance of skin temperature in the regulation of sweating", Journal of Applied Physiology, Vol. 31, Issue 1, 80-87, July 1, 1971