In the general population, sweat is about 99 percent water with one percent minerals and other compounds. One small study (n=7) found that sweat contains trace amounts of metals, including sodium, potassium, calcium, copper, magnesium, and zinc, after the subjects had completed a long bout of exercise in exposed heat. (2) The amount of these substances also varies among individuals. A 2004 study on 26 Turkish wrestlers found similar composition with the additional of iron and chromium. But these listed substances are NOT toxins. Within a healthy range, these minerals are essential to maintain normal health. Our body also sweats out water-soluble vitamins, such as C and riboflavin. (3)
Of course, our body may contain a minute amount of chemicals that we cannot process, but our body excretes these substances out of our sweat glands or urinary tract anyways. Examining the past and current evidence of sweating can help us de-myth some of the beliefs about sweating and “toxins” and better understanding how perspiration works.
Research in perspiration in the early 20th century had found a number of toxic chemicals that the body excretes, such as chlorine. A review published in 1934 identified two such studies of water poisoning among men who performed hard labor while drinking unclean water. (4) Industrial and environmental workers who were exposed to various hazardous chemicals, such as arsenic and mercury, had significant levels of such metals in their sweat. (5) In this Canadian systematic review, the authors argue that such population may benefit from sweating while in a sauna or engage in exercise to help rid of such metals. For many of us who are not exposed to such metals in our environment or handle such materials everyday, we may not need to worry about this.
Another Canadian study also found that phthalates, a flexible compound that makes up the flexibility and durability of plastic, are found in the sweat samples among their small sample of subjects (n=20). Yet this compound was not found in the blood samples, which was hypothesized that sweating is a way the body removes phthalates from the bloodstream. (6)
So should we be concerned about this? Probably not, considering that this is an enormous topic that goes beyond the scope of this article and even our practice. Without proper training and better understanding of human physiology, it is not our responsibility to make pseudo-diagnosis about whether our clients or patients have “toxins” or not. Even if they have, how do we know? How do we measure it? Is it within our scope of practice?
Despite the benefits of sweating that has a strong likelihood of removing unwanted substances in our body, there are some drawbacks if we sweat too much for too long. Two Taiwanese studies found that excessive sweating during exercise — in these cases, badminton and tennis — can decrease uric acid excretion in urine and increase the level of uric acid in the blood. Not a good thing, especially if you're not rehydrating during exercise. (7,9) Such in increase in uric acid may increase the risks of getting neuropathic disorders among type II diabetes. (8)
1. Gorski D. Fashionably Toxic. Science-based Medicine. Sept 2014.
2. Montain SJ, Cheuvront SN, Lukaski HC. Sweat mineral-element responses during 7 h of exercise-heat stress. Int J Sport Nutr Exerc Metab. 2007 Dec;17(6):574-82.
3. Mickelsen O, Keys A. The Composition of Sweat, With Special References to the Vitamins. Journal of Biological Chemistry. 1943, 149:479-490.
4. McSwiney BA. The Composition of Human Perspiration (Samuel Hyde Memorial Lecture): (Section of Physical Medicine). Proceedings of the Royal Society of Medicine. 1934;27(7):839-848.
5. Sears ME, Kerr KJ, Bray RI. Arsenic, Cadmium, Lead, and Mercury in Sweat: A Systematic Review. Journal of Environmental and Public Health. 2012;2012:184745. doi:10.1155/2012/184745.
6. Genuis SJ, Beesoon S, Lobo RA, Birkholz D. Human Elimination of Phthalate Compounds: Blood, Urine, and Sweat (BUS) Study. The Scientific World Journal. 2012;2012:615068. doi:10.1100/2012/615068.
7. Huang LL, Huang CT, Chen ML, Mao IF. Effects of profuse sweating induced by exercise on urinary uric acid excretion in a hot environment. Chin J Physiol. 2010 Aug 31;53(4):254-61.
8. Papanas N, Demetriou M, Katsiki N, et al. Increased Serum Levels of Uric Acid Are Associated with Sudomotor Dysfunction in Subjects with Type 2 Diabetes Mellitus. Experimental Diabetes Research. 2011;2011:346051. doi:10.1155/2011/346051.
9. Huang CT, Chen ML, Huang LL, Mao IF. Uric acid and urea in human sweat. Chin J Physiol. 2002 Sep 30;45(3):109-15.