The facial sweat of a boy
Perspiration (sweating, transpiration, or diaphoresis) is the production of fluids secreted by the sweat glands in the skin of mammals.
Two types of sweat glands can be found in humans: Eccrine glands and apocrine glands. The eccrine sweat glands are distributed over much of the body.
In humans, sweating is primarily a means of thermoregulation which is achieved by the water-rich secretion of the eccrine glands. Maximum sweat rates of an adult can be up to 2-4 liters per hour or 10-14 liters per day (10-15 g/min•m²) Evaporation of sweat from the skin surface has a cooling effect due to the evaporation of water. Hence, in hot weather, or when the individual's muscles heat up due to exertion, more sweat is produced. 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, relatively few, such as humans and horses, produce large amounts of sweat in order to cool down.
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. When men and women exercise at the same absolute intensity there are no differences in sweating responses.
- Hypohidrosis is decreased sweating from whatever cause.
- Focal hyperhidrosis is increased or excessive sweating in certain regions such as the underarms, palms, soles, face or groin.
- Hyperhidrosis, also referred to as generalized or secondary hyperhidrosis is excessive sweating due to an underlying condition and usually involves the body as a whole.
- Hidromeiosis is a reduction in sweating that is due to blockages of sweat glands in humid conditions.
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.
Sweating causes a decrease in core temperature through evaporative cooling at the skin surface. As high energy molecules evaporate from the skin, releasing energy absorbed from the body, the skin and superficial vessels decrease in temperature. Cooled venous blood then returns to the body's core and counteracts rising core temperatures.
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.
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. During average intensity exercise, sweat losses can average up to 2 litres of water/hour. 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.
Sweat contains mainly water. It also contains minerals, lactate, and urea. Mineral composition varies with the individual, their acclimatisation to heat, exercise and sweating, the particular stress source (sauna, etc.), the duration of sweating, and the composition of minerals in the body. An indication of the minerals content is sodium (0.9 gram/liter), potassium (0.2 g/l), calcium (0.015 g/l), magnesium (0.0013 g/l). Also many other trace elements are excreted in sweat, again an indication of their concentration is (although measurements can vary fifteenfold) zinc (0.4 milligrams/liter), copper (0.3–0.8 mg/l), iron (1 mg/l), chromium (0.1 mg/l), nickel (0.05 mg/l), lead (0.05 mg/l). Probably many other less-abundant trace minerals leave the body through sweating with correspondingly lower concentrations. Some exogenous organic compounds make their way into sweat as exemplified by an unidentified odiferous "maple syrup" scented compound in several of the species in the mushroom genus Lactarius. In humans, sweat is hypoosmotic relative to plasma  (i.e. less salty). Sweat typically is found at moderately acidic to neutral pH levels, typically between 4.5 and 7.0.
See also 
- Mosher HH (1933). "Simultaneous Study of Constituents of Urine and Perspiration". The Journal of Biological Chemistry 99 (3): 781–790.
- Jessen,C., Temperature regulation in humans and other mammals, Springer, Berlin, 2000, 193 pp
- Mack,G.W. and Nadel,E.R., Body fluid balance during heat stress in humans. In: Fregly,M.J., Blatteis,C.M. (Eds.), Handbook of physiology. Section 4: Environmental physiology, Oxford University Press, New York, 1996, pp. 187-214
- Sawka,M.L., Wenger,C.B., and Pandolf,K.B., Thermoregulatory responses to acute exercise-heat stress and heat acclimation. In: Fregly,M.J., Blatteis,C.M. (Eds.), Handbook of phys
- 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 (in Undetermined) 29 (1): 58–60. PMID 13066656.
- Robertshaw D, Taylor CR (November 1969). "Sweat gland function of the donkey (Equus asinus)". The Journal of Physiology 205 (1): 79–89. PMC 1348626. PMID 5347721.
- McDonald RE, Fleming RI, Beeley JG, et al. (2009). "Latherin: A Surfactant Protein of Horse Sweat and Saliva". In Koutsopoulos, Sotirios. PLoS ONE 4 (5): e5726. doi:10.1371/journal.pone.0005726. PMC 2684629. PMID 19478940.
- "Women outshine men in sweat test". Sydney Morning Herald. 9 October 2010. Retrieved 21 October 2010.
- Academy of Hyperhidrosis
- Parsons K (2009). Maintaining health, comfort and productivity in heat waves 2. doi:10.3402/gha.v2i0.2057. PMC 2799322. PMID 20052377. Unknown parameter
- Kameia, Tomoya; Tsudab, Takao; Kitagawab, Shinya; Naitoha, Ken; Nakashimaa, Koji; Ohhashi, Toshio (June 1998). "Physical stimuli and emotional stress-induced sweat secretions in the human palm and forehead". Analytica Chimica Acta 365 (1–3): 319–326. doi:10.1016/S0003-2670(97)00642-9.
- "Sweat mineral-element responses during 7 h of exercise-heat stress," Int J Sport Nutr Exerc Metab 2007 Dec;17(6):574-82.
- Cohn JR, Emmett EA (1978). "The excretion of traces of metals in human sweat". Annals of Clinical and Laboratory Science 8 (4): 270–5. PMID 686643.
- Saraymen, Recep; Kılıç, Eser; Yazar, Süleyman (2004). "Sweat Copper, Zinc, Iron, Magnesium and Chromium Levels in National Wrestler". İnönü Üniversitesi Tıp Fakültesi Dergisi 11 (1): 7–10.
- Aurora, David "Lactarius fragilis" Mushrooms Demystified 1986 Ten Speed Press, Berkeley California
- Constanzo, Linda S. BRS Physiology (4th ed.). p. 155.
- Bandodkar AJ, Hung VWS, Jia W, Ramirez GV, Windmiller JR, Martinez AG, Ramirez J, Chan G, Kagan K, Wang J (2013). "Tattoo-based potentiometric ion-selective sensors for epidermal pH monitoring". Analyst 138 (1): 123–8.
Further reading 
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- 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. doi:10.1016/S0190-9622(89)70063-3. PMID 2654204.
- Ferner S, Koszmagk R, Lehmann A, Heilmann W (1990). "[Reference values of Na(+) and Cl(-) concentrations in adult sweat]". Zeitschrift Für Erkrankungen Der Atmungsorgane (in German) 175 (2): 70–5. PMID 2264363.
- 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. PMID 5556967.