Studies on sweating. V. Studies of quantity and distribution of thermogenic sweat delivery to the skin

A century of exercise physiology: concepts that ignited the study of human thermoregulation. Part 2: physiological measurements

In this, the second of four historical reviews on human thermoregulation during exercise, we examine the research techniques developed by our forebears. We emphasise calorimetry and thermometry, and measurements of vasomotor and sudomotor function. Since its first human use (1899), direct calorimetry has provided the foundation for modern respirometric methods for quantifying metabolic rate, and remains the most precise index of whole-body heat exchange and storage. Its alternative, biophysical modelling, relies upon many, often dubious assumptions. Thermometry, used for >300 y to assess deep-body temperatures, provides only an instantaneous snapshot of the thermal status of tissues in contact with any thermometer. Seemingly unbeknownst to some, thermal time delays at some surrogate sites preclude valid measurements during non-steady state conditions. To assess cutaneous blood flow, immersion plethysmography was introduced (1875), followed by strain-gauge plethysmography (1949) and then laser-Doppler velocimetry (1964). Those techniques allow only local flow measurements, which may not reflect whole-body blood flows. Sudomotor function has been estimated from body-mass losses since the 1600s, but using mass losses to assess evaporation rates requires precise measures of non-evaporated sweat, which are rarely obtained. Hygrometric methods provide data for local sweat rates, but not local evaporation rates, and most local sweat rates cannot be extrapolated to reflect whole-body sweating. The objective of these methodological overviews and critiques is to provide a deeper understanding of how modern measurement techniques were developed, their underlying assumptions, and the strengths and weaknesses of the measurements used for humans exercising and working in thermally challenging conditions.

Sex-related differences in sudomotor function in healthy early twenties focused on activated sweat gland density

The purpose of this study was to quantitatively assess the difference in sudomotor function between healthy males and females in their early twenties by measuring skin surface area and activated sweat gland density (ASGD). The quantitative sudomotor axon reflex test (QSART), a method for evaluating autonomic nervous system activity, was used for quantification. In QSART, the sweat glands are activated directly or indirectly by the subcutaneous application of neurotransmitters, such as acetylcholine, through iontophoresis. This series of mechanisms is called the sudomotor axon reflex. After recording age, height, weight, and several measurements of the forearm, QSART was performed on 101 healthy controls aged 21-26 years to measure ASGD. The mean temperature and humidity on the measurement days were 11.4°C and 58.1% on May 3, 2018, and 14.7°C and 70.3% on May 10, 2018. The result of independent sample t-test showed higher ASGD in women (P < 0.05). The body surface area and the surface area of the forearms were higher in men (P < 0.001), but the number of activated sweat glands was not significantly different according to sex. The activated sweat gland counts of the body and forearms were analyzed through linear regression by age for males and females. Except for the activated sweat gland count of the male body, the analysis showed a tendency to decrease with increasing age but was not statistically significant in any case (P > 0.05). Showing insufficient coefficient of determination (R²), multiple regression analyses with sex and ages did not correct this insignificance between age and activated sweat gland count.

Thermogenic and psychogenic sweating in humans: Identifying eccrine glandular recruitment patterns from glabrous and non-glabrous skin surfaces

In this experiment, psychogenic (mental arithmetic), thermogenic (mean body temperature elevation of 0.6 °C) and combined thermo-psychogenic treatments were used to explore eccrine sweat-gland recruitment from glabrous (volar hand and forehead) and non-glabrous skin surfaces (chest). It was hypothesised that each treatment would activate the same glands, and that glandular activity would be intermittent. Nine individuals participated in a single trial with normothermic and mildly hyperthermic phases. When normothermic, a 10-min arithmetical challenge was administered, during which sudomotor activity was recorded. Following passive heating and thermal clamping, sweating responses were again evaluated (10 min). A second arithmetical challenge (10 min) was administered during clamped hyperthermia, with its sudorific impact recorded. The activity of individual sweat glands was recorded at 60-s intervals, using precisely positioned, and uniformly applied, starch-iodide papers. Those imprints were digitised and analysed. Peak activity typically occurred during the thermo-psychogenic treatment, revealing physiologically active densities of 128 (volar hand), 165 (forehead) and 77 glands.cm^-2 (chest). Except for the hand (46%), glands uniquely activated by one treatment were consistently <10% of the total glands identified. Glandular activations were most commonly of an intermittent nature, particularly during the thermogenic treatment. Accordingly, we accepted the hypothesis that psychogenic, thermogenic and thermo-psychogenic stimuli activate the same sweat glands in both the glabrous and non-glabrous regions. In addition, this investigation has provided detailed descriptions of the intermittent nature of sweat-gland activity, revealing that a consistent proportion of the physiologically active glands are recruited during these thermal and non-thermal stimuli.

Hyperhidrosis: A Case Study and Theoretical Formulation

A case study is presented of a 20-year-old male who experienced marked increases in body temperature and profuse sweating of the forehead and trunk when in formal social situations. No other physiological nor psychological manifestations of anxiety were admitted to and no situational avoidance was reported. Pretreatment, posttreatment, and follow-up self-report measures and daily self-monitoring of intensity and frequency of sweating were collected to evaluate treatment effects. Treatment was conducted over a period of 20 weeks. Cued conditioning and desensitisation were initially employed, however treatment effect was difficult to determine. The effects of an inadvertent in vivo exposure in week 6 of treatment and the subsequent change in treatment to exposure and cognitive therapy are discussed. The positive effects of treatment, which led to a decrease in the frequency and intensity of the sweating response, were evident at the completion of treatment and well maintained at 60 weeks follow-up. The use of exposure and cognitive therapy as a suitable treatment for this disorder are discussed in light of other anxiety disorders.

Influence of systemic corticotherapy on the triggering of pityriasis versicolor

Pityriasis versicolor is a frequent mycosis and the use of systemic corticotherapy is one of its predisposing factors. This is an observational, cross-sectional, analytical and comparative study, conducted from January 2012 to January 2013 in the following outpatient clinics: Dermatology Service, Cassiano Antonio Moraes Hospital (HUCAM), Vitória, ES, Brazil; Nephrology Service, HUCAM; and Leprosy Department, Maruípe Health Unit, Vitória, ES, Brazil. Patients, undergoing long-term systemic corticotherapy (or not), were assessed with respect to the presence of pityriasis versicolor. If there was mycosis, a direct mycological examination would be carried out. The spss 17.0 software was used for the statistical analysis. From the total of 100 patients, nine had pityriasis versicolor, being eight from the corticotherapy group and one from the group with no use of corticosteroids. Regarding the patients with mycosis, the prevalent age ranged from 20 to 39 years, with six patients; six were women; seven mixed race; eight were undergoing long-term systemic corticotherapy; seven were taking low-dose systemic corticosteroids; four had leucocytosis; five had normal total cholesterol and triglycerides; and four had normal glycaemia. There was increased frequency of pityriasis versicolor in the group undergoing systemic corticotherapy with statistical significance, corroborating the only study on the topic (1962).

Regional variations in transepidermal water loss, eccrine sweat gland density, sweat secretion rates and electrolyte composition in resting and exercising humans

Literature from the past 168 years has been filtered to provide a unified summary of the regional distribution of cutaneous water and electrolyte losses. The former occurs via transepidermal water vapour diffusion and secretion from the eccrine sweat glands. Daily insensible water losses for a standardised individual (surface area 1.8 m2) will be 0.6-2.3 L, with the hands (80-160 g.h-1) and feet (50-150 g.h-1) losing the most, the head and neck losing intermediate amounts (40-75 g.h-1) and all remaining sites losing 15-60 g.h-1. Whilst sweat gland densities vary widely across the skin surface, this same individual would possess some 2.03 million functional glands, with the highest density on the volar surfaces of the fingers (530 glands.cm-2) and the lowest on the upper lip (16 glands.cm-2). During passive heating that results in a resting whole-body sweat rate of approximately 0.4 L.min-1, the forehead (0.99 mg.cm-2.min-1), dorsal fingers (0.62 mg.cm-2.min-1) and upper back (0.59 mg.cm-2.min-1) would display the highest sweat flows, whilst the medial thighs and anterior legs will secrete the least (both 0.12 mg.cm-2.min-1). Since sweat glands selectively reabsorb electrolytes, the sodium and chloride composition of discharged sweat varies with secretion rate. Across whole-body sweat rates from 0.72 to 3.65 mg.cm-2.min-1, sodium losses of 26.5-49.7 mmol.L-1 could be expected, with the corresponding chloride loss being 26.8-36.7 mmol.L-1. Nevertheless, there can be threefold differences in electrolyte losses across skin regions. When exercising in the heat, local sweat rates increase dramatically, with regional glandular flows becoming more homogeneous. However, intra-regional evaporative potential remains proportional to each local surface area. Thus, there is little evidence that regional sudomotor variations reflect an hierarchical distribution of sweating either at rest or during exercise.

Skin of color: biology, structure, function, and implications for dermatologic disease

People with skin of color constitute a wide range of racial and ethnic groups-including Africans, African Americans, African Caribbeans, Chinese and Japanese, Native American Navajo Indians, and certain groups of fair-skinned persons (eg, Indians, Pakistanis, Arabs), and Hispanics. It has been predicted that people with skin of color will constitute a majority of the United States and international populations in the 21st century. There is not a wealth of data on racial and ethnic differences in skin and hair structure, physiology, and function. What studies do exist involve small patient populations and often have methodologic flaws. Consequently, few definitive conclusions can be made. The literature does support a racial differential in epidermal melanin content and melanosome dispersion in people of color compared with fair-skinned persons. Other studies have demonstrated differences in hair structure and fibroblast size and structure between black and fair-skinned persons. These differences could at least in part account for the lower incidence of skin cancer in certain people of color compared with fair-skinned persons; a lower incidence and different presentation of photo aging; pigmentation disorders in people with skin of color; and a higher incidence of certain types of alopecia in Africans and African Americans compared with those of other ancestry. However, biologic or genetic factors are not the only ones impacting on these differences in dermatologic disorders. Cultural practices also can have a significant impact. Further studies are needed to help dermatologists optimally treat people with skin of color.

Using human sweat to extract chromium from chromite ore processing residue: applications to setting health-based cleanup levels

Chromite ore processing residue (COPR) containing measurable levels of hexavalent and trivalent chromium. [Cr(VI) and Cr(III), respectively] has been used to fill in low-lying areas in Hudson County, N.J. While it has been demonstrated that direct dermal contact with solutions containing Cr(VI) may elicit allergic contact dermatitis (ACD) in previously sensitized individuals, it is unknown to what degree skin moisture may solubilize Cr(VI) from COPR adhering to skin. An accurate estimate of this extraction potential is necessary to establish COPR concentrations of Cr(VI) and Cr(III) that are protective of eliciting ACD in sensitized individuals. The purpose of this study was to measure the extractable fraction of Cr(VI) and total chromium [Cr(III) and Cr(VI)] in soils impacted by COPR using human sweat as the extractant. Human sweat was collected from seven male volunteers. Samples of COPR material containing the following Cr(VI) and total chromium concentrations were collected: Cr(VI), 16, 136, and 1240 ppm; total chromium, 932 and 6660 ppm. The samples were sieved to obtain a uniform particle size < 500 microns. The samples were then mixed with human sweat at 30 degrees C for 12 h, after which the sweat was filtered and analyzed to determine the dissolved concentration of Cr(VI) and total chromium. The data from these analyses show that no detectable levels (limit of detection = 0.010 ppm) of Cr(VI) were leached from COPR containing 16 ppm Cr(VI). At Cr(VI) concentrations of 136 and 1240 ppm, less than 0.1% of the Cr(VI) present in the COPR sample was extracted into sweat, and sweat concentrations were 0.133 ppm Cr(VI) or less. Similarly, the amount of Crtotal extracted was 0.3% or less at COPR concentrations as high as 6600 ppm Crtotal, and sweat concentrations were 2.3 ppm Crtotal or less. If a minimum concentration of 10 ppm (Bagdon and Hazen, 1991) to 54 ppm (Paustenbach et al., 1992) Cr(VI) in sweat is required to elicit an ACD response in chromium-sensitive individuals, the current study results suggest that a COPR Cr(VI) concentration of at least 10,000-54,000 ppm would be required to elicit ACD. If 500 ppm (or greater) of solubilized Cr(III) is required to elicit an ACD response (NJDEPE, 1992a), then a COPR concentration of 250,000 ppm Cr(III) or greater would be required to elicit an allergic response. These results suggest that ACD is unlikely to occur as a result of environmental exposure to the COPR.

Sweat gland disturbances in granuloma annulare and necrobiosis lipoidica

We studied sweat gland distribution, density and activity in thirteen cases of granuloma annulare and ten cases of necrobiosis lipoidica, using a combination of the plastic impression and starch-iodine methods. The pattern of sweat gland disturbance in the two diseases was entirely different. In necrobiosis lipoidica an intense and uniform hypohidrosis was detected throughout the lesion, whereas in granuloma annulare the disturbance followed the morphology of the lesion (the papular border showed complete anhidrosis, whereas the flat central part of the lesion showed only moderate hypohidrosis or normal sweating). The method assigns numerical values to the 'relative density' and the 'relative activity' of the functioning sweat glands compared with normal skin, thus permitting statistical evaluation of the results.

Black and white human skin differences

This review of black and white human skin differences emphasizes the alleged importance of factors other than the obvious, i.e., skin color. Physicochemical differences and differences in susceptibility to irritants and allergens suggest a more resistant black than white skin. Differences appear to exist in the frequency of which several skin diseases occur among blacks and whites. A striking feature in this literature is the disagreement between authors. Common for much of this information is difficulty of interpretation, because of socioeconomic influences and other environmental factors.