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"Sweat" redirects here. For other uses, see Sweat (disambiguation).
Perspiration

The facial sweat of a runner
ICD-10 R61
ICD-9 780.8

Sweating (perspiration, or diaphoresis) is a process of excretion, the production of a fluid, sweat consisting primarily of water as well as various dissolved solids (chiefly chlorides), that is excreted by the sweat glands in the skin of mammals.[1] Sweat contains the chemicals or odorants 2-methylphenol (o-cresol) and 4-methylphenol (p-cresol), as well as a small amount of urea.

In humans, sweating is primarily a means of thermoregulation, although it has been proposed that components of male sweat can act as pheromonal cues.[2] Trace amount of toxins are excreted through perspiration.

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 like those of humans. Although sweating is found in a wide variety of mammals,[3][4] relatively few, such as humans and horses, produce large amounts of sweat in order to cool down.[5]

A study has discovered that men, on average, start perspiring much more quickly than women, then twice as much when they are in the middle of exercising at the same relative intensity.[6] When men and women exercise at the same absolute intensity there are no differences in sweating responses.

Definition

  • Hypohidrosis is decreased sweating from whatever cause[7]
  • Hyperhidrosis is increased sweating from whatever cause[7]
  • Hidromeiosis is a reduction in sweating that is due to blockages of sweat glands in humid conditions.[8]

Mechanism

File:Demonstration of Sweat.jpg

Sweating allows the body to regulate its temperature. Sweating is controlled from a center in the preoptic and anterior regions of the brain's hypothalamus, where thermosensitive neurons are located. The heat-regulatory function of the hypothalamus is also affected by inputs from temperature receptors in the skin. High skin temperature reduces the hypothalamic set point for sweating and increases the gain of the hypothalamic feedback system in response to variations in core temperature. Overall, however, the sweating response to a rise in hypothalamic ('core') temperature is much larger than the response to the same increase in average skin temperature. The process of sweating decreases core temperature, whereas the process of evaporation decreases surface temperature.

There are two situations in which the nerves will stimulate the sweat glands, causing perspiration: during physical heat and during emotional stress. In general, emotionally induced sweating is restricted to palms, soles, armpits, and sometimes the forehead, while physical heat-induced sweating occurs throughout the body.[9]

Sweat is not pure water; it always contains a small amount (0.2–1%) of solute. When a person moves from a cold climate to a hot climate, adaptive changes occur in the sweating mechanisms of the person. This process is referred to as acclimatisation: the maximum rate of sweating increases and its solute composition decreases. The volume of water lost in sweat daily is highly variable, ranging from 100 to 8,000 mL/day. The solute loss can be as much as 350 mmol/day (or 90 mmol/day acclimatised) of sodium under the most extreme conditions. In a cool climate and in the absence of exercise, sodium loss can be very low (less than 5 mmols/day). Sodium concentration in sweat is 30-65 mmol/l, depending on the degree of acclimatisation.

See also

References

  1. Mosher HH (1933). Simultaneous Study of Constituents of Urine and Perspiration. The Journal of Biological Chemistry 99 (3): 781–790.
  2. Wyart C, Webster WW, Chen JH, et al. (February 2007). Smelling a single component of male sweat alters levels of cortisol in women. The Journal of Neuroscience 27 (6): 1261–5.
  3. Goglia G (January 1953). [Further research on the branched sweat glands in some mammals (Cavia cobaya, Sus scrofa, Equus caballus).]. Bollettino Della Società Italiana Di Biologia Sperimentale 29 (1): 58–60.
  4. Robertshaw D, Taylor CR (November 1969). Sweat gland function of the donkey (Equus asinus). The Journal of Physiology 205 (1): 79–89.
  5. McDonald RE, Fleming RI, Beeley JG, et al. (2009). Latherin: a surfactant protein of horse sweat and saliva. PLoS ONE 4 (5): e5726.
  6. includeonly>"Women outshine men in sweat test", Sydney Morning Hearld, 9 October 2010. Retrieved on 21 October 2010.
  7. 7.0 7.1 [1]
  8. Parsons K (2009). Maintaining health, comfort and productivity in heat waves. Glob Health Action 2.
  9. (June 1998). Physical stimuli and emotional stress-induced sweat secretions in the human palm and forehead. Analytica Chimica Acta 365 (1-3): 319–326.

Further reading

  • Sato K, Kang WH, Saga K, Sato KT (April 1989). Biology of sweat glands and their disorders. I. Normal sweat gland function. Journal of the American Academy of Dermatology 20 (4): 537–63.
  • Ferner S, Koszmagk R, Lehmann A, Heilmann W (1990). [Reference values of Na(+) and Cl(-) concentrations in adult sweat]. Zeitschrift Für Erkrankungen Der Atmungsorgane 175 (2): 70–5.
  • Bindner. Solutions and treatments for extreme perspiration and sweating. Internet recource.
  • Nadel ER, Bullard RW, Stolwijk JA (July 1971). Importance of skin temperature in the regulation of sweating. Journal of Applied Physiology 31 (1): 80–7.
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