Arsenic, cadmium, lead, and mercury exposures are ubiquitous. These toxic elements have no physiological benefits, engendering interest in minimizing body burden. The physiological process of sweating has long been regarded as “cleansing” and of low risk. Reports of toxicant levels in sweat were sought in Medline, Embase, Toxline, Biosis, and AMED as well as reference lists and grey literature, from inception to March 22, 2011. Of 122 records identified, 24 were included in evidence synthesis. Populations, and sweat collection methods and concentrations varied widely. In individuals with higher exposure or body burden, sweat generally exceeded plasma or urine concentrations, and dermal could match or surpass urinary daily excretion. Arsenic dermal excretion was severalfold higher in arsenic-exposed individuals than in unexposed controls. Cadmium was more concentrated in sweat than in blood plasma. Sweat lead was associated with high-molecular-weight molecules, and in an interventional study, levels were higher with endurance compared with intensive exercise. Mercury levels normalized with repeated saunas in a case report. Sweating deserves consideration for toxic element detoxification. Research including appropriately sized trials is needed to establish safe, effective therapeutic protocols.
No person is without some level of toxic metals in their bodies, circulating and accumulating with acute and chronic lifetime exposures. An individual may take numerous measures to minimize exposures and to optimize metabolism and excretion of toxic elements in the stool and urine with diet, supplements, and chelation therapy [
Sweating with heat and/or exercise has been viewed throughout the ages, by groups worldwide, as “cleansing.” As part of a scoping review regarding arsenic, cadmium, lead, and mercury, we reviewed the scientific literature pertaining to toxicant excretion in sweat.
While many chemical elements are essential for life, arsenic, cadmium, lead, and mercury have no known beneficial effect in humans. On the contrary, all four elements are confirmed or probable carcinogens, and they exhibit wide-ranging toxic effects on many bodily systems, including the nervous, endocrine, renal, musculoskeletal, immunological, and cardiovascular systems [
Children and the fetus are most at risk of harm, with early exposures potentially predisposing the youngster over his/her lifetime to multisystem ailments, as well as lower IQ and dysfunctional behavior. In older populations there is increased likelihood of early cognitive decline, as well as a range of conditions including kidney and cardiovascular disease, diabetes, and osteoporosis [
Some populations are exposed to elevated levels of toxic elements by virtue of geochemistry, resulting in groundwater or foods with elevated levels of toxic elements (e.g., elevated arsenic in groundwater, most famously in parts of Asia such as Bangladesh but also elsewhere; cadmium that accumulates in foods grown in particular locations with high levels in soils or from fertilizers, including shellfish [
With toxic elements ubiquitous in our air, water, food, and the physical environment, as well as in many consumer products, prudent avoidance is not always possible. Although signs and symptoms of chronic disease are consistent with effects of arsenic, cadmium, lead, and/or mercury, physicians commonly have a low index of clinical suspicion, and therefore levels of toxic elements are seldom investigated. Diagnosis may be challenging because multiple chemicals may contribute to subtle effects in chronic illnesses of an individual, and the effects may be synergistic. A recent review called for mercury assessment in all patients presenting with hypertension or any vascular disease [
Increasing the thermal load on the body activates heat loss mechanisms including increased circulation throughout the skin and sweating [
Eccrine sweat is produced in tubular coil glands under the skin surface in response to heat and, or work stress. Capillaries as well as adjacent adipose tissue may contribute to secretions from sebaceous and apocrine glands, as has been seen in research using sweat patches to detect drugs of abuse [
Children, with greater surface area in comparison to body mass, have been observed in research studies to sweat less than adults, with sweating increasing through puberty [
Medline, Embase, Toxline, Biosis, and AMED were searched, with no restriction on date or language, to March 22, 2011. These records were supplemented with searches for other research by key authors, searches of citations and reference lists of key reports, and “related articles.”
Neither sweating nor toxic elements are exclusively modern topics of research, so in order to search older literature for all chemical forms, the online version of the Chemical Rubber Company Handbook was searched for all arsenic, cadmium, lead, and mercury compounds, and lists of keywords were extracted from these lists. Searches using these keywords yielded records that were not identified in searches using the four chemical abstracts service (CAS) numbers or the medical subject headings (MeSHs) for arsenic, cadmium, lead, and mercury. CAS numbers and MeSHs are intended for specific individual chemicals or records referring to unspecified compounds—the tool cannot simultaneously be both specific and general. Toxic element records were searched for terms related to sweating, perspiration, sauna, steam baths, exercise, depuration, and secretion or excretion from skin. Bibliographic records were imported, duplicates were removed, and reports were screened using Zotero 2.03 (
Titles and abstracts were screened by one investigator (MS), for primary reports with data on one or more of the toxic elements in sweat, with at least a substantial abstract in English. Reviews were included at this level, to search reference lists. Two investigators (MS and KK) independently screened studies for inclusion, and extracted and verified data. All studies presenting quantitative human data on levels of arsenic, cadmium, lead, and/or mercury were included, regardless of experimental design, or methods of sweat collection or chemical analysis.
Of 122 bibliographic records identified, 70 did not meet inclusion criteria at first screening, 52 full-text articles were sought for full-text screening, and 50 were obtained and screened. Data from the extended abstract of a report in German [
PRISMA flow diagram of evidence searches and inclusion.
Along with essential minerals, sweat is an acknowledged excretory route for toxic metals. For instance, it is recommended to sample hair close to the scalp because content of toxic elements may be elevated along the shaft, from either environmental contamination or excreted toxins in sweat and sebum [
Studies of excretion of arsenic in sweat.
Study | Country, participants | Study design and intervention | Key findings (concentrations of |
---|---|---|---|
Yousuf et al. 2011 [ | Bangladesh | Secretions from chest, back, and abdomen collected for 24 h, on gauze pads (8-fold; 2 × 3 inches) attached to fitted T-shirt | As secretion severalfold greater for As-exposed groups |
Genuis et al. 2010 [ | Canada | Simultaneous measurement of As in blood plasma, urine, and sweat | 17 participants with As detected in all samples |
Studies of cadmium excretion in sweat.
Study | Country, participants | Study design and intervention | Key findings (concentrations |
---|---|---|---|
Genuis et al., 2010 [ | Canada | Simultaneous measurement of toxic trace elements in blood plasma, urine, and sweat | 3 participants with cadmium detected in all samples |
Omokhodion and Howard, 1994 [ | UK | Sweat collected using modified arm bag (hand excluded) | Cadmium detected in 13 sweat samples |
Stauber and Florence, 1988 [ | Australia | Forearm sweat induced by pilocarpine iontophoresis and collected on a membrane filter | Males mean sweat cadmium 1.4 (range <0.5–10) |
Stauber and Florence, 1987 [ | Australia | Forearm sweat induced by pilocarpine iontophoresis and collected on a membrane filter | Cadmium not detected in sweat (0.5 detection limit) |
Robinson and Weiss, 1980 [ | USA | Exercise and shower preceded sauna for sweat collection. Sweat collected as drips from forehead or nose | Sweat cadmium (range 11–200) |
Robinson and Weiss, 1980 [ | USA | As previous, cadmium also measured in hair segments. | Daily excretion of cadmium estimated as follows: |
Cohn and Emmett, 1978 [ | USA | Total body washdown and arm bag techniques | Mean concentration of cadmium in sweat > urine |
Studies of lead excretion in sweat.
Study | Country, participants | Study design and intervention | Key findings (concentrations |
---|---|---|---|
Genuis et al., 2010 [ | Canada | Analyses of blood plasma, urine, and sweat | Sweat mean 31 (range 1.5–94) ( |
Omokhodion and Crockford, 1991 [ | UK | Blood, urine, and sweat lead measured before and following ingestion of lead chloride: 1 or 2 doses of lead chloride (20 mg PbCl2 total, in 1 or 2 divided doses). | Blood lead peaked at 4 h |
Omokhodion and Howard, 1991 [ | Unidentified “tropics” | Measured lead in sweat, blood, and urine simultaneously | Workers: |
Omokhodion and Crockford, 1991 [ | UK | Measured lead in sweat, urine, blood, and saliva | (i) Blood lead 86 (range 60–140) |
Parpaleĭ et al., 1991 [ | Russia | NR in abstract | “… sauna increased excretion with sweat fluid of toxic substances [lead] that penetrated the body during work. Sauna is recommended.” |
Lilley et al., 1988 [ | Australia | Lead dust 6 h/day for 4 days 20 mg Pb dust on L arm of volunteer | Sweat lead in workers: 71–18,000 |
Stauber and Florence, 1988 [ | Australia | Sweating induced on the forearms by pilocarpine iontophoresis and collected on a membrane filter | Mean sweat lead: |
Stauber and Florence, 1987 [ | Australia | Sweating induced in the forearms by pilocarpine iontophoresis and collected on a membrane filter | No significant differences among groups |
Haber et al., 1985 [ | Germany | Comparison of precisely defined physical work (intensive cycling and extended rowing in a pool), examining lead excretion in persons with elevated blood levels compared with nonexposed controls | Aerobic endurance training (rowing) caused a significant drop in the blood lead level in the occupationally exposed group (mean 430 (range 320–580) decreased to 370 (240–450)) ( |
Cohn and Emmett, 1978 [ | USA | Total body washdown and arm bag techniques | The mean concentration of lead in sweat was similar to that in urine |
Hohnandel et al., 1973 [ | 33 healthy males | 15 min of arm bag collection | Mean sweat lead: |
Studies of mercury excretion in sweat.
Study | Country, participants | Study design and intervention | Key findings (concentrations |
---|---|---|---|
Genuis et al., 2010 [ | Canada | Sweating induced by exercise or sauna, collected directly into bottle | 16 participants had mercury detected in all samples |
Robinson and Skelly, 1983 [ | USA | Mercury in sweat dripping from forehead or nose, compared with urine | Sweat mean 0.5 (range 0.1–1.4) |
Sunderman 1978 [ | USA | Case report of chelating agents to treat mercury intoxication, followed by a regimen of daily sweat and physiotherapy for a protracted period of several months | Appreciable quantities of mercury were excreted in sweat. |
Lovejoy et al., 1973 [ | USA | Participants wore rubber chest waders from 7 : 30 to 9 : 00 am | Exposed workers: |
Arsenic, cadmium, lead, and mercury may be excreted in appreciable quantities through the skin, and rates of excretion were reported to match or even exceed urinary excretion in a 24-hour period. This is of particular interest should renal compromise limit urinary excretion of toxic elements.
Most of the research identified was over 20 years old, and collection methods varied widely. Although authors described thorough precleaning methods, sweat concentrations measured in research settings are not well validated and varied according to the location on the body, collection method, and from day to day according to other variables such as hydration. Sweat contains metals not only from the blood plasma, but also evidently originating from dermal layers (particularly with significant dermal exposures, as for workers in welding, smelting, or battery manufacturing). It would appear that large variabilities in measured concentrations, apart from collection methods as mentioned above, were likely the result of differences in excretion amongst widely varying individuals with ranges of body burdens, genetic polymorphisms affecting detoxification efficiency, and physiological states, coupled with necessarily crude if simple experimental techniques. These variations were very much greater than would be expected due to limitations of analytical methods. Although analytical methods have improved over the years, analysis of these metals was commonplace at the time of the studies. Authors generally reported analytical methods rigorously or provided references to thorough descriptions and included internal standards and some indication of sensitivity.
The observation that between a third and a half of lead in sweat may be associated with high-molecular-weight molecules [
Yousuf et al.’s recent study demonstrating a 2 : 1 molar ratio of zinc : arsenic and increased vitamin E in skin secretions suggests potential therapeutic supplementation to accommodate these biochemical requirements. Vitamin E, zinc, and other nutrients are required for methylation and detoxification of arsenic within the body, and vitamin E supplementation improves the skin manifestations in arsenicosis [
From an occupational health perspective, lead, and presumably other toxic elements, may be absorbed via the skin, which supports showering at work and further suggests the possibility of purging workers’ skin by washing with a chelating agent (e.g., EDTA rinses extracted lead from workers’ skin in methods validation experimentation [
Sweating has long been perceived to promote health, not only accompanying exercise but also with heat. Worldwide traditions and customs include Roman baths, Aboriginal sweat lodges, Scandinavian saunas (dry heat; relative humidity from 40% to 60%), and Turkish baths (with steam). Infrared saunas heat exposed tissues with infrared radiation, while air temperatures remain cooler than in other saunas.
Sweating is a long-standing, if recently forgotten, aspect of mercury detoxification. Various strategies used to maintain the mercury mining workforce have been explored over the centuries. In Spain and colonies, long the western world’s primary sources of mercury, sending ill workers to warmer climes away from the exposure to drink weak beer (the hydrogen peroxide catalase oxidation of elemental mercury to ionic mercury is competitively inhibited by alcohol, increasing mercury in exhaled breath [
With acclimatization and regular use, the sauna is generally well tolerated by all ages [
Optimizing the potential of sweating as a therapeutic excretory mechanism merits further research. To date, the large body of research into homeostasis of the most common metals (sodium, potassium, and to a lesser extent, magnesium, calcium, and zinc) and conditioning or adaptation to regular sweating by athletes has not been matched with studies of excretion of trace elements. Limited research suggests indirectly that conditioning may not restrict excretion of nonessential elements. Combination therapies, such as administration of
It has been noted that among people whose health is compromised by toxicants, heat regulatory mechanisms of the autonomic nervous system are often affected, resulting in a failure to sweat readily [
For biomonitoring and research purposes, modern validated methods are desirable to collect and measure elements in sweat, so this means of excretion may be considered in the context of other measures such as urine, blood, feces, and hair concentrations. Considerations for dry and wet collection methods were recently discussed in the context of essential solutes [
Undoubtedly further research in this area would improve understanding, but the available evidence suggests that physicians could consider recommending sweating as tolerated via exercise (preferred) and/or use of a sauna as a low-risk, potentially beneficial treatment for individuals who may be experiencing effects of toxic elements, or for individuals with regular exposure to or accretion of toxicants.
Sweating offers potential and deserves consideration, to assist with removal of toxic elements from the body. As toxic elements are implicated in many serious chronic conditions, research is needed in patients with select conditions to evaluate the body burden and to test the efficacy of source removal, dietary choices and supplements, interventions that induce sweating, and treatments with drugs, all to enhance excretion of toxic elements with the goal of clinical improvement. There is a clear need for robust trials, appropriately sized to assess clinical outcomes, from which therapeutic protocols can be derived. Both biochemical and clinical outcomes should be examined in order to develop and monitor clinical interventions that are both safe and effective.
The authors declare that they have no conflicts of interests.
The scoping review from which this work is derived was generously supported by a grant from the Canadian Institutes of Health Research, and the Social Sciences and Humanities Research Council of Canada. There are no conflicts of interest.