What type of secretion is perspiration

Formula diet: Upper arm: 47 vs. Figure 4. Eccrine sweat composition Methodological considerations In science, the accuracy and reliability of study methodology are critical to interpret results and draw conclusions about the impact of an intervention or other factor on the outcome measure of interest. Overview of sweat composition Sweat is a very complex aqueous mixture of chemicals. Sodium chloride It is well established that sweat [Na] and [Cl] can vary considerably among individuals.

Figure 5. Effect of sweat flow rate Sodium chloride Sweat flow rate is another important factor determining final sweat [Na] and [Cl] and of other aspects of sweat composition.

Figure 6. Figure 7. Figure 8. Figure 9. Bicarbonate, pH, and lactate In addition to Na and Cl conservation, another important function of the sweat gland is reabsorption of bicarbonate for the maintenance of acid-base balance of the blood [ 8 ]. Sweat composition as a biomarker There has been considerable interest recently in the use of sweat as a non-invasive alternative to blood analysis to provide insights to human physiology, health, and performance. Skin health Eccrine sweat is thought to play a role in epidermal barrier homeostasis through its delivery of water, natural moisturizing factors, and antimicrobial peptides to the skin surface.

Role in micronutrient balance Sweat gland adjustments in response to deficiency or excess Heat acclimation Sodium chloride The changes in sweat [Na] and [Cl] during heat acclimation have been well established and reviewed in previous papers [ , ] and therefore will not be comprehensively discussed here.

Trace minerals A common question on the topic of heat acclimation is whether or not electrolytes or minerals other than NaCl are conserved. Diet Sodium chloride It is a common perception that Na ingestion influences sweat [Na] or the rate of sweat Na excretion. Trace minerals Several studies have investigated the hypothesis that dietary intake of trace minerals and vitamins influences sweat composition. Sweating-induced deficiencies Sodium chloride Of all the substances lost in sweat, Na and Cl are lost in the highest concentrations.

Trace minerals and vitamins There have been some suggestions that athletes may require dietary supplementation of certain trace minerals due in part to excessive losses in sweat. Comparison of sweat gland and kidney function Water conservation and excretion The sweat glands are often compared to the nephrons of the kidneys, whose main function, among others, is to conserve the vital constituents of the body [ ].

Excretion of toxicants The notion that sweating is a means to accelerate the elimination of persistent environmental contaminants from the human body has been around for many years [ , ]. Excretion of metabolic waste Another important function of the kidneys is excretion of metabolic and dietary waste products. Altered sweat gland function from conditions and medications As shown in Table 6 , certain medical conditions and medications can impact sweating rate and sweat composition.

Table 6. Conditions and medications that alter sweat gland function. Etiology involves neurogenic overactivity of otherwise normal sweat glands [ 3 , 29 ]; associated with genetic predisposition [ , ]. Tattoos Chronic Reduced sweating rate and higher sweat [Na] in response to pharmacologically-induced local sweating than non-tattooed skin; unknown etiology [ — ]. More research involving exercise or heat-induced whole body sweating is needed.

Conclusions This paper discussed sweat gland physiology and the state of the evidence regarding various roles of sweating and sweat composition in human health. Based on this review of the literature, the following conclusions were drawn: It is well established that eccrine sweat glands have a tremendous capacity to secrete sweat for the liberation of heat during exercise and exposure to hot environments. Fluid needs for training, competition, and recovery in track-and-field athletes.

Fluid balance, hydration, and athletic performance. Biology of sweat glands and their disorders. Disorders of sweat gland function. J Am Acad Dermatol. Encapsulated environment. Compr Physiol. The physiology and pharmacology of the eccrine sweat gland In: Goldsmith L, editor.

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Pflugers Arch. Rapid regulation of electrolyte absorption in sweat duct. J Membr Biol. Hydrogen ion and electrolyte excretion of the single human sweat gland. The effect of intracutaneous d-aldosterone and hydrocortisone on human eccrine sweat gland function.

Sodium secretion and reabsorption in the human eccrine sweat gland. J Clin Invest. Glucose metabolism of the isolated eccrine sweat gland. The relation between glucose metabolism and sodium transport. The secretion of salt and water by the eccrine sweat gland.

Arch Dermatol. Local control of eccrine sweat gland function. Fed Proc. Effect of local heating and arterial occlusion on sweat electrolyte content. J Appl Physiol. Observations on lactate content of sweat.

Sweating responses during changes of hypothalamic temperature in the rhesus monkey. Skin blood flow and local temperature independently modify sweat rate during passive heat stress in humans. Importance of skin temperature in the regulation of sweating. Peripheral modifications to the central drive for sweating. Evidence that transient changes in sudomotor output with cold and warm fluid ingestion are independently modulated by abdominal, but not oral thermoreceptors. Staying warm in the cold with a hot drink: the role of visceral thermoreceptors.

Does intramuscular thermal feedback modulate eccrine sweating in exercising humans? Acta Physiol Oxf. Stimulation of pentose cycle in the eccrine sweat gland by adrenergic drugs. Integrated physiological mechanisms of exercise performance, adaptation, and maladaptation to heat stress. Mechanisms and controllers of eccrine sweating in humans. Front Biosci Schol Ed.

Non-thermoregulatory modulation of sweating in humans. Exerc Sport Sci Rev. Function of human eccrine sweat glands during dynamic exercise and passive heat stress.

Regional differences in the effect of exercise intensity on thermoregulatory sweating and cutaneous vasodilation. Acta Physiol Scand. Effects of training, environment, and host factors on the sweating response to exercise. Int J Sports Med. Control of sweating rate while exercising in the heat.

Med Sci Sports. Plasma aldosterone and sweat sodium concentrations after exercise and heat acclimation. Influence of acclimatization on sweat sodium concentration. Thermoregulatory responses of middle-aged and young men during dry-heat acclimation.

Human heat acclimitization. Indianapolis: Benchmark Press; Maximal oxygen uptake, sweating and tolerance to exercise in the heat. Int J Biometeorol. Exercise- and methylcholine-induced sweating responses in older and younger men: effect of heat acclimation and aerobic fitness.

Effects of ageing and physical training on the peripheral sweat production of the human eccrine sweat gland. Age Ageing. Effect of physical training on peripheral sweat production. Human heat adaptation. Skin blood flow and sweating changes following exercise training and heat acclimation. Mechanisms of thermal acclimation to exercise and heat. Long distance runners present upregulated sweating responses than sedentary counterparts. PLoS One. Adaptive modifications in the thermoregulatory system of long-distance runners.

Cholinergic sensitivity of the eccrine sweat gland in trained and untrained men. Thermoregulatory and blood responses during exercise at graded hypohydration levels. Control of thermoregulatory sweating is altered by hydration level and exercise intensity. Effect of hyperosmolality on control of blood flow and sweating. Local sweating responses of different body areas in dehydration-hydration experiments. J Physiol Paris. Divergent roles of plasma osmolality and the baroreflex on sweating and skin blood flow.

Plasma hyperosmolality augments peripheral vascular response to baroreceptor unloading during heat stress. Effect of blood volume on sweating rate and body fluids in exercising humans. Sweating as a heat loss thermoeffector. Handb Clin Neurol. Eccrine sweating and mortality during heat waves in very young and very old persons. Isr J Med Sci.

Methylcholine-activated eccrine sweat gland density and output as a function of age. Longitudinal effects of age on heat-activated sweat gland density and output in healthy active older men. Age-related decrements in heat dissipation during physical activity occur as early as the age of Sweat responses in the aged. Regional differences in the sweating responses of older and younger men. Regional differences in age-related decrements of the cutaneous vascular and sweating responses to passive heating.

Nonuniform, age-related decrements in regional sweating and skin blood flow. Mechanisms underlying the age-related decrement in the human sweating response. Invited review: aging and human temperature regulation. Comparison of thermoregulatory responses to exercise in dry heat among prepubertal boys, young adults and older males. Exp Physiol. Sweating and skin blood flow during exercise: effects of age and maximal oxygen uptake.

The effect of ageing and fitness on thermoregulatory response to high-intensity exercise. Scand J Med Sci Sports. Thermoregulation at rest and during exercise in healthy older adults In: Holloszy JO, editor. Exercise and sport sciences reviews. Responses of older and younger women to exercise in dry and humid heat without fluid replacement. Med Sci Sports Exerc. Sex differences in acetylcholine-induced sweating responses due to physical training. J Physiol Anthropol.

Sex differences in postsynaptic sweating and cutaneous vasodilation. Sex differences in thermoeffector responses during exercise at fixed requirements for heat loss. Sex modulates whole-body sudomotor thermosensitivity during exercise. J Physiol. Exercise and the Female. A Life Span Approach. Body mapping of sweating patterns in athletes: a sex comparison. American college of sports medicine position stand. Exercise and fluid replacement.

Physiological responses of men and women to prolonged dry heat exposure. Aviat Space Environ Med. Physiological responses of men and women to humid and dry heat. The relative influence of physical fitness, acclimatization state, anthropometric measures and gender on individual reactions to heat stress.

Variations in body morphology explain sex differences in thermoeffector function during compensable heat stress. Sex hormone effects on autonomic mechanisms of thermoregulation in humans. Auton Neurosci. Modeling of gender differences in thermoregulation. Mil Med. A review of comparative responses of men and women to heat stress.

Environ Res. Reproductive hormone influences on thermoregulation in women. Does sex have an independent effect on thermoeffector responses during exercise in the heat? Thermoregulation during exercise in the heat in children: old concepts revisited. Sweat electrolyte loss during exercise in the heat: effects of gender and maturation. Sweat gland response to exercise in the heat among pre-, mid-, and late-pubertal boys.

Local sweating and cutaneous blood flow during exercise in hypobaric environments. Effect of acute normobaric hypoxia on peripheral sweat rate. High Alt Med Biol. The influence of acute and 23 days of intermittent hypoxic exposures on the exercise-induced forehead sweating response. Eur J Appl Physiol. Nocturnal lowering of thresholds for sweating and vasodilation. Menstrual cycle phase and time of day alter reference signal controlling arm blood flow and sweating.

Sex- and menstrual cycle-related differences in sweating and cutaneous blood flow in response to passive heat exposure. Effects of physical training on heat loss responses of young women to passive heating in relation to menstrual cycle.

Control of sweating during the human menstrual cycle. Thermoregulation and the menstrual cycle. Effect of the menstrual cycle on performance of intermittent, high-intensity shuttle running in a hot environment. Exercise performance over the menstrual cycle in temperate and hot, humid conditions.

Menstrual cycle phase does not modulate whole body heat loss during exercise in hot, dry conditions. Humid heat stress affects trained female athletes more than does their menstrual phase.

Individual variations in structure and function of human eccrine sweat gland. Sports Med. Minimal sodium losses through the skin. Chemical composition of sweat. Physiol Rev. Loss of minerals through the skin of normal humans when sweating is avoided.

Characterization of sweat induced with pilocarpine, physical exercise, and collected passively by metabolomic analysis. Skin Res Technol. Metabolomics analysis of human sweat collected after moderate exercise. The proteomic and metabolomic characterization of exercise-induced sweat for human performance monitoring: A pilot investigation.

Dissolution of materials in artificial skin surface film liquids. Toxicol In Vitro. Sweat lactate in man is derived from blood glucose. Stress biomarkers in biological fluids and their point-of-use detection. ACS Sens. Quantification of cortisol in human eccrine sweat by liquid chromatography - tandem mass spectrometry.

Formulation and stability of a novel artificial human sweat under conditions of storage and use. Whole body sweat collection in humans: an improved method with preliminary data on electrolyte content. Oxford textbook of sports medicine. Comparison of regional patch collection vs. Variations in regional sweat composition in normal human males.

Sweat composition in exercise and in heat. Body map of regional versus whole body sweating rate and sweat electrolyte concentrations in men and women during moderate exercise-heat stress.

Low abundance of sweat duct Cl- channel CFTR in both healthy and cystic fibrosis athletes with exceptionally salty sweat during exercise. Factors influencing chloride concentration in human sweat. Osmotic pressure of human sweat. Changes in composition of sweat during acclimatization to heat.

Changes in the index of sweat ion concentration with increasing sweat during passive heat stress in humans. You may opt-out of e-mail communications at any time by clicking on the Unsubscribe link in the e-mail. Our Housecall e-newsletter will keep you up-to-date on the latest health information. Mayo Clinic does not endorse companies or products.

Advertising revenue supports our not-for-profit mission. Any use of this site constitutes your agreement to the Terms and Conditions and Privacy Policy linked below. Mayo Clinic is a nonprofit organization and proceeds from Web advertising help support our mission. Mayo Clinic does not endorse any of the third party products and services advertised. There are two to four million sweat glands distributed all over our bodies. Eccrine glands secrete an odorless, clear fluid that helps the body to control its temperature by promoting heat loss through evaporation.

In general, the type of sweat involved in hyperhidrosis is eccrine sweat. Apocrine glands are found in the armpits and genital region. They produce a thick fluid. Both the eccrine and apocrine sweat glands are activated by nerves. In people who have excessive sweating or hyperhidrosis , the sweat glands eccrine glands in particular overreact to stimuli and are just generally overactive, producing more sweat than is necessary.

It's often said that people with hyperhidrosis have sweat glands that are stuck in the "on" position. Ready to learn more about hyperhidrosis? Nevertheless, across laboratories, one may perhaps consider that such data may better represent sweat rates that would obtain under clothing, particularly multi-layered ensembles, and may therefore be considered to be of greater utility for such applications.

The water vapour content of a gas may be measured using a range of methods. For instance, one can extract water vapour through its condensation within chilled tubes[ 44 ] or its absorption into desiccants e. However, these methods are somewhat slow and can lack precision due to the incomplete removal of water vapour[ 46 ].

Since water vapour absorbs infrared radiation and also alters the thermal conductivity of a dry gas, then it is possible to determine the water vapour content of an air sample through changes in its infrared light absorption[ ] or its thermal conductivity[ ]. Nevertheless, neither of these techniques has become popular. Others adopted the approach of quantifying evaporative heat exchange from changes within the water vapour pressure gradient of the boundary layer air[ , ].

While this technique has a broad application, it is not well suited to high sweat rates. The contemporary hygrometric methods of choice for mechanistic research, where precision in both timing and quantification are required, rely upon the effect of water vapour on electrical resistance[ — ] and capacitance[ , ], or on the dew point of the gas sample[ , ].

Of these methods, capacitance hygrometry seems superior since capacitors are linear across a broad humidity range, and they possess a faster response time when water vapour in the air sample is decreasing[ ].

Nevertheless, for each of these techniques, capsules of varying size e. To avoid pressure artefacts, an adhesive should be used to make an air-tight seal e. Air at room temperature, and with a constant and low humidity often dry gas , is pumped into the capsule and across the skin surface at a fixed flow.

This flow is regulated to sustain a dry skin surface forced evaporation and thereby optimises the operating range of the hygrometer so that it matches the anticipated local sweat rate. The humidity and temperature of the effluent air are then measured either within or at some point downstream of the sweat capsule[ — ].

These procedures keep the layer of air next to the skin dry and constantly moving, and this not only facilitates transepidermal water loss, but also increases evaporation. This may amplify local sweating reactive error , relative to that which may have been observed from the naked skin[ ]. In fact, computations of total sweat rate from regional measures generally exceed mass changes[ ]. However, the skin below a capsule may be slightly cooler than the adjacent skin surfaces due to greater local evaporation, if the latter is measured without air movement.

This can suppress local secretion. Thus, like the patch technique, some localised influences may encourage, whilst others may subdue sweating. Nevertheless, Kenefick et al. Therefore, on balance, one may reasonably assume that, while the sweat patch technique is perhaps closer to the fully clothed state, sweat capsules using flows of mL.

Missing from this discussion is experimental evidence relating to regional differences in evaporative heat loss. Readers will know that evaporation does not always match local sweat rates, and whilst the perspective presented within this contribution is focussed upon mechanisms that modulate sweating and its regional variations, there is a gap in our knowledge relating to local evaporation rates. During thermoneutral rest, the data presented above for transepidermal water loss Figure 1 , in combination with the specific latent heat of vaporisation, permit one to compute local heat losses.

However, for exercising states, local heat losses remain unknown. Since one cannot reliably determine whole-body sweat rates from indiscriminately chosen local sweat flows, then it would be equally imprecise to approximate whole-body evaporative heat loss from either local sweating or evaporative rates. A wide range of pharmacological and non-thermal influences can stimulate active sweat secretion, but our focus is limited to thermal sweating.

Since glandular densities vary across body regions, then if each gland possessed an identical secretion rate, one could assume that inter-regional variations in discharged sweat would be a simple function of eccrine gland density.

However, during passive thermal and exercise stimulations, eccrine glands from different regions discharge sweat at vastly different rates, both across and within individuals[ 65 , 85 ]. From this evidence, it is apparent that regional variations in secretion can be ascribed to both anatomical and physiological variations. When active thermal sweating commences, it generally does so through the low-level and gradual recruitment of eccrine glands[ , ], and subsequently through elevated glandular flows[ 64 , 87 , ].

During isometric exercise, for example, the activation of silent sweat glands is the principal means through which intensity-dependent increases in sweat secretion from both the glabrous and non-glabrous skin surfaces are achieved[ 82 ].

However, some glands do not remain constantly active within a region. Indeed, while the number of active glands may be increasing with thermal loading, these are not always the same glands[ 3 , , ], with some even decreasing their activity over time[ 88 ]. This general recruitment pattern was illustrated by Buono[ 89 ] in exercising subjects across six sites, with each displaying a gradual, yet variable, elevation in the number of activated sweat glands as core temperature climbed. This recruitment pattern seems not to be affected by ageing, with glandular flows being reduced[ ] whilst the number of activated sweat glands appears to remain constant.

However, Kondo et al. When the timing of sweat gland recruitment was compared across skin regions in resting, heated individuals, Kuno[ 2 , 3 ] reported a simultaneous glandular activation from all regions except the palmar and plantar surfaces.

Kuno[ 2 ] referred to Oehler[ ], who is believed to have been first to claim, following visual inspection, that glandular recruitment progressed over the body surface. However, Kuno and his associates[ 3 ] found no evidence for a recruitment pattern other than its ubiquitous and simultaneous appearance, regardless of how thermal loading was applied. Contemporaneously, List and Peet[ ] used colorimetry painted iodine solution to record regional sudomotor activation during passive heating with 0.

From these qualitative methods, they observed considerable recruitment variability across subjects. It seemed that, in some, sweating commenced on the face forehead and upper lip , whilst in others, it occurred first at the axillae and inguinal folds. They noted that in most individuals, however, sweating commenced on the face and torso before it appeared on the extremities.

However, Hertzman et al. Nonetheless, close examination of that manuscript reveals that neither sudomotor activation nor sweat gland recruitment was measured. Instead, recruitment was determined from changes in the slopes of curves fitted to data points obtained from trials performed in summer and winter, with each point representing a single trial mean. More than 20 air temperatures were evaluated across 61 trials using 22 participants.

Thus, these curves summarised group data, and it is uncertain whether data for different skin regions were obtained from the same individuals.

Given the wide inter-individual variability in sweating, it is not unreasonable to suggest that such data are less than ideal for drawing such an interpretation. In a later experiment[ ], starch-iodide papers were positioned over different skin surfaces of an unspecified number of resting supine heated subjects.

No group data were provided to support the dermatomal recruitment hypothesis. Instead graphs for two individuals that displayed this glandular recruitment pattern were published, along with another for an individual with a different pattern. The same group later provided supporting evidence from two more individuals[ ]. Certainly time delays between the dorsal foot surface and the forehead are evident within both papers[ , ], but one struggles to resolve time differences among some sites.

Moreover, one might contest that, while the dermatomal recruitment of sweating may indeed occur, the data presented did not provide unequivocal support for that hypothesis. It is perhaps time to revisit this theory, but with careful consideration of the postural and pressure affects on sweating. Notwithstanding the possibility of a centrally determined sweat recruitment pattern, once activated, a cannulated sweat gland will reveal both a gradually rising column of sweat and a rhythmical rise and fall of this fluid.

This was first described by Takahara[ ] for individual glands, and was thought to be due to pulsatile contractions of the myoepithelium and induced via changes in sympathetic tone[ ]. This rhythm is synchronised within and across body regions[ , , , ] and is clearly of autonomic origin, having a period of 0. This synchrony is illustrated in Figure 3 , in which discharged sweat rates were simultaneously recorded from glabrous hairless and non-glabrous foot surfaces.

Since these data were derived using sweat capsules 3. Nevertheless, clear sudomotor synchronisation is evident across all sites. Such synchrony between glabrous and non-glabrous surfaces has previously been described[ ], though it is not always evident[ , ], and it demonstrates the existence of neural linkages with the hypothalamus.

The synchronous nature of sweating across skin sites. Data are from one individual, collected using ventilated capsules 3. Curves have been adjusted vertically to reduced overlap and to highlight secretory synchronisation. There are many studies in which sweat secretion from several sites has been simultaneously measured, and it is from this research that we have extracted data to describe the regional distribution of thermal sweating. To the best of our knowledge, the first such report during resting thermal loading was by Ikeuchi and Kuno[ 43 ], while the corresponding quantification during exercising states appears to be that of Weiner[ ].

Over the ensuing years, 16 suitable resting studies and 20 exercising studies were identified in which inter-regional variations in sweat secretion were evaluated. These data were pooled for the current analyses. Data from men and women were combined, with only adults being included. A broad range of thermal stimuli were applied, and subjects were tested in different postures seated, supine.

In the exercising studies, both dynamic arm cranking, bench stepping, cycling, running and static handgrip, leg extension exercise was performed. When data were available across different thermal or exercise conditions, only the more stressful states were selected.

Finally, data were collected using various sweat collection techniques filter papers, sweat capsules, sweat patches. With the exception of exercise states, no effort was made to tease out non-thermal influences. Instead, it was deemed to be more generally useful if integrated analyses were undertaken.

Therefore, regional variations for this thermoeffector function, during both exogenous passive and endogenous thermal loading, will be described for the same 14 sites used to summarise sweat gland densities.

Across all studies and skin sites, the mean resting sweat rate was 0. The limitations of such an integrated analysis are widely accepted. However, it was considered that both the depth and breadth of these resources could act to negate many of these drawbacks, and that such an analysis may have broad appeal and application for readers. In the next section, data drawn from experiments conducted using more rigidly controlled experimental conditions and methods are reported and compared with these data.

For this exercise, the transepidermal water loss data described above were combined with thermal sweating data to provide regional variations in total cutaneous water loss Figure 4 A. In addition, by combining functional gland density data, which were assumed to reflect those recruited during resting and exercising states, regional sweat gland outputs flows were computed Figure 4 B.

In the current analyses, data sets were used across all sites, providing data from individuals studied at rest, and with the number of region-specific data sets ranging from just two for the buttocks[ 43 , 45 ] through to 21 at the face, which included the forehead, cheeks, chin and upper lip.

These extant data clearly support the classical conclusion that discharged sweat flow varies across the skin surface of resting subjects[ 2 ]. However, the cause of this variation has not been isolated. For instance, while differences between precursor sweat production and reabsorption within the sweat duct determine discharged secretion, as will regional deviations in glandular density and cholinergic sensitivity, regional variations in these attributes have not yet been explored.

Total cutaneous water loss and sweat gland outputs in resting, passively heated individuals. A Regional variations in total cutaneous water loss descending order and B sweat gland output ordered as in A. A is a summation of transepidermal water loss averaged from Figure 1 : dorsal foot was assumed to equal the dorsal hand and thermoregulatory sweating. For simplicity, all anterior surfaces of the head were included within the face. For the limbs, data from all surfaces were combined, while the hands and feet were separated according to their dorsal and volar surfaces, with corresponding data obtained from the fingers and toes included within those surfaces.

Data for the buttocks came from only two studies with considerable between-study variability and should be treated cautiously. B shows variations in sweat gland output, derived by combining data from Figures 2 B and 4 A. Data from one notable resting study[ 74 ] were not included in this analysis since the investigators used a sweat box, from which the neck and head protruded, eliciting considerable bias in torso secretion relative to that of the head.

Whilst there was considerable variation in the distribution of sweating among studies for physiological and perhaps also some methodological reasons, the consensus from these analyses is that the torso back and head face surfaces have the highest local sweat rates, whilst sites located on the limbs, particularly the feet soles , secrete the least sweat during passive thermal stimulation.

For the most part, however, sweating appears to be relatively homogeneously distributed. The volar surfaces of the hands and feet, which have the highest glandular densities, possess the lowest glandular flows during resting thermal stimulation, although these sites clearly respond to passive heating[ 61 , 62 ].

In comparison with the torso sites chest, back , they have about five times more sweat glands, yet sweat gland output from the torso glands is approximately 7—15 times greater depending upon which sites are compared. Indeed, there is a clear variability in the regional distribution of sweat gland output. For most sites, this pattern is consistent with their local sweat secretion Figure 4.

However, the face produces 4—7 times greater glandular flow relative to the palms and soles, but it has only half the glandular density.

These differences reflect variations in contributions to heat dissipation. This generalisation appears somewhat paradoxical when one considers the hands and feet, since their volar surfaces have very low sweat gland outputs.

Thus, their particularly high activated glandular densities appear to compensate for these low flows, permitting their potential heat loss to be proportional to their surface areas, at least when resting. This observation is of significance when one considers the thermolytic potential of these appendages. During exercise, endogenous heat production increases, as does the demand for evaporative cooling, and non-thermal stimuli will now affect both sudomotor and vasomotor functions.

It is possible that neural feedforward central command , which emanates from the rostral brain and simultaneously activates the motor and sympathetic neurons, elevates the sensitivity of the sweating mechanism[ , ].

Therefore, in heated resting humans, the initiation of exercise is accompanied by reduced skin blood flow and increased sweating[ , ]. The question of interest now centres upon whether or not the distribution of sweating observed at rest is retained during exercise.

This conclusion is consistent with the resting data presented in Figure 4 and Table 3 , and it also matches, at least qualitatively, the current distillation for exercise which involved different individuals and separate data sets Figure 5. On this basis, one may conclude that exercise is not associated with a redistribution of sweating, but it is instead accompanied by an almost universal elevation in sweat gland output, such that glandular output becomes more homogeneous across the body surface, even though some regions still have greater secretion rates.

Total cutaneous water loss and sweat gland output during dynamic and static exercise. A is a summation of transepidermal water loss averaged from Figure 1 : dorsal foot was assumed to equal the dorsal hand and thermal and non-thermal sweating. For the limbs, data from all surfaces were combined, while the hands and feet were separated according to their dorsal and volar surfaces, with data obtained from the fingers and toes included within those surfaces. Data for the buttocks came from only one study.

B shows variations in sweat gland output, derived by combining data from Figures 2 B and 5 A. Sources: Taylor et al. There are inherent limitations to using retrospective data. While the impact of this is reduced as the size of the database grows, this does not generally apply to intra-regional comparisons since the number of data sets available for these sites is very much smaller.

Ideally, such data should be drawn from experiments in which variability, due to differences in experimental design, is minimal. In this regard, readers are also directed to the research of Smith and Havenith[ ], and these observations were incorporated into the above analysis Figure 5 A.

However, due to methodological differences gravimetric versus hygrometric , they are not included within the analyses below, which focus wholly on data from the authors' laboratory, in which the distribution of sweating was investigated across 45 sites, some of which have not previously been described[ 61 , 62 , , , ].

In the latter studies, trials terminated with core temperatures ranging from To avoid a temperature bias, the water-perfusion suit was not in contact with skin surfaces from which local sweating was measured. To facilitate a first-stage comparison of these data with those reported within the previous section Figures 4 and 5 , site-specific data for the same 14 sites were assembled and presented in Figure 6 A rest and B exercise beside data from the literature.

Whilst data from the authors' research were also included within that obtained from the literature Figures 4 and 5 , such relationships permit greater faith in the retrospective analysis of these data.

Comparisons among the regional distributions of eccrine sweating. A At rest and B during exercise. Values distilled from the literature are also contained within Figures 4 and 5 and are duplicated here in descending order within each graph for ease of comparison.

Data from authors' laboratory Wollongong: sweat capsules capacitance hygrometry were collected from the studies reported in Figures 7 and 8 but grouped to match the target 14 regions. Having established this broad inter-investigation agreement, we will now present data from our own research that pertain specifically to intra-regional variations in sweating. These data were collected using standardised conditions and methods, and quantify sudomotor variability under both resting Figure 7 : 45 sites and exercising states Figure 8 : 26 sites.

In the latter case, data were averaged across work rates to provide integrated sweat rates at a mean external load of W. However, these data were not collected for limb segments other than the hands and feet. A few subjects participated in several, but not all trials. Inter- and intra-regional distribution of steady-state thermal sweating ventilated capsules for resting individuals. Data are means with standard deviations extracted from five studies undertaken within the authors' laboratory sweat capsules capacitance hygrometry.

Sources: Machado-Moreira et al. Inter- and intra-regional distribution of steady-state sweating during exercise. B For comparative purposes, averages extracted from the literature for exercise triangles are provided sources identified in Figure 5.

Data reported by Smith and Havenith[ ] second exercise intensity are also provided open circles. Included within Figure 8 are data from two other sources. For some sites forehead, chest, palm and four foot surfaces , there is strong agreement across these independent studies. Values for another seven sites fall within one standard deviation. However, data for each of the seven hand sites represent considerable under-estimations of the local sweat rates obtained using ventilated capsules, even given the inherent reactive errors associated with each method.

Values for the scalp, upper back and abdomen are also lower, but not dramatically so. The third data set presented in Figure 8 comes from the literature Figure 5 : triangles , with sweat rates from only two sites falling beyond the one standard deviation limit forehead and dorsal hand.

One may confidently conclude from Figures 5 , 6 , 7 and 8 that these data provide similar and valid representations of the distribution of human eccrine sweating. It is evident from Figures 7 and 8 that the site-specific maximal-to-minimal sweat rates differed by a factor of 8 during resting exposures forehead 0. These ranges are certainly of practical benefit, but they may also have mechanistic utility. For instance, it has been reported that the volar surfaces of the hand do not participate in thermal sweating[ , ].

Clearly, this interpretation is wrong. Indeed, there are 11 sites that sweat less profusely than the palms during passive heating: four leg, five thigh and two head sites. In addition, one wonders whether or not there might be a physiological basis for this regional mosaic of sweat secretion, such as a preferential distribution to optimise heat loss efficiency across body segments and surfaces.

Since sweating subserves thermal homeostasis, then some insight into this question may be gained from an analysis of the corresponding evaporative potential of each site and combinations of sites, assuming uniform regional skin wettedness, skin temperatures, wind speed and mass transfer coefficients.

Of course, these simplifications deviate from reality, but they permit one to consider states within which evaporative heat loss is optimised and modulated primarily by the autonomic control of thermal sweating. Accordingly, these first-principles calculations, whether performed using the regional sweat rates extracted from the 30 investigations reported in Figures 4 and 5 , or just the data within Figures 7 and 8 , show a remarkable consistency with the size of each surface area represented by these skin regions.

For example, of the 14 regions described in Table 2 , the five with both the highest evaporative heat loss potential at rest Table 3 also had the greatest skin surface areas Table 2.

In descending order, these were the back, thigh, leg, head and abdomen. During exercise, the following order was realised: back, thigh, head, leg and chest. From a regulatory perspective, one must conclude that this evidence fails to lend support to an hierarchical configuration of regional sweating in either condition.

Indeed, higher secretion rates at any one site would seem merely to reflect that site approaching its full potential for evaporative heat loss for the existing conditions. Furthermore, following heat adaptation, skin regions further away from their site-specific, maximal sweating capacity similarly experience the greatest increase in sweat secretion[ ].

With respect to the impact of sweating on the design of clothing and sweating, thermal manikins, the following generalisations may be drawn from the data presented in this section concerning sweat rates observed during exercise. However, both the dorsal and volar aspects of the fingers sweat quite profusely Figures 7 and 8 , while the palms are far less responsive. The authors assumed that readers would come to this paper from varied backgrounds and interests.

With this in mind, the possibility was considered that some, armed only with a knowledge of body surface area, may wish to know eccrine glandular densities for specific regions or site-specific sweat rates during rest and exercise.

To address this possibility, Table 4 was constructed, with regression coefficients enabling a first-level prediction of these variables.

To illustrate this, prediction equations for the head are highlighted below:. Detailed treatment of this topic is beyond the scope of this review, and readers are directed to the literature e. However, having described the distribution of eccrine sweat glands and secretion rates during thermal loading, it seems reasonable to include a brief consideration of electrolyte loss since sweat composition[ — ], and therefore cutaneous water vapour pressure[ 32 , ] are influenced by intra-glandular water turnover.

Thus, sodium and chloride sweat losses vary in relation to sweat gland output[ — ], but not that of potassium and calcium, which seem to be inversely related to flow[ 7 ]. This renders the modelling of sweat composition more complex.

Indeed, when one realises that sweat sodium concentrations, for instance, can double in some individuals over the physiological range for sweat production[ — ], then it becomes apparent that quoting sweat compositions without simultaneously reporting glandular or whole-body sweat flow offers little useful information.

There are many reports that describe the composition of sweat. From these, six were identified that provided both whole-body electrolyte losses and sweat rates[ , — ]. In some cases, whole-body sweat rates were not provided but could be calculated, and it was found to vary between 0. Nevertheless, these studies indicate that, when sweating within this zone, the whole-body sodium loss could be expected to fall within the range of Of course, it is recognised that electrolyte losses are widely variable across[ ] and within individuals[ , ].

Thirteen papers were identified that provided simultaneous sweat secretion and composition data for several of the 14 body regions of interest. These data are summarised in Figure 9 and Table 5 and, with the exception of the thigh, provide a reasonable reflection of regional variations in electrolyte losses over the flows indicated Table 5.

These data tend to over-estimate whole-body electrolyte concentrations and, like local sweat rates, should generally not be used to approximate whole-body losses[ ], although some sites do lend themselves to such use[ , ]. Regional variations in sweat sodium, chloride and potassium concentrations.