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Sauna Hype

Twenty people collected their own sweat, and the authors reported more of several toxic metals in it than in urine

The Blood, Urine and Sweat (BUS) series compared the three fluids in the same people, and this 2011 paper in Archives of Environmental Contamination and Toxicology came first. Its sweat figures still circulate as evidence that sweating clears metals.

The paper

Blood, Urine, and Sweat (BUS) Study: Monitoring and Elimination of Bioaccumulated Toxic Elements

Genuis SJ, Birkholz D, Rodushkin I, Beesoon S. Archives of Environmental Contamination and Toxicology, 2011;61(2):344-357.

Read the paper ↗PubMed 21057782 ↗

See the study at a glance

Design
Cross-sectional biomonitoring study
People
20 adults
Who they were
Ten healthy adults and 10 with various health problems. A 2012 paper from the same project describes 10 of its 20 participants as patients recruited from the first author's clinical practice.
What they did
Each person gave one sample each of sweat, blood and urine, and the lab tested them for about 120 compounds. People worked up a sweat by exercising or sitting in a steam or infrared sauna, and they collected it themselves.
How long
One sample of each fluid per person

These numbers came out of it

20

Twenty people took part, and each collected one sweat sample themselves.

~120

The lab looked for about 120 compounds in each person's samples.

31 vs 1.8

A 2012 review's tables put mean lead at 31 µg/L in sweat and 1.8 µg/L in urine.

The researchers did this

Genuis and colleagues gathered one sample each of sweat, blood and urine from 20 adults and tested them for about 120 compounds.Source 1 · Cross-sectional studyBlood, Urine, and Sweat (BUS) Study: Monitoring and Elimination of Bioaccumulated Toxic ElementsGenuis SJ, Birkholz D, Rodushkin I, et al.. Archives of Environmental Contamination and Toxicology, 2011.Read the paper ↗PubMed ↗ Ten of the participants were healthy and 10 had various health problems. They worked up a sweat by exercising or sitting in a steam or infrared sauna, and they collected the sweat themselves.

The abstract says many toxic elements "appeared to be preferentially excreted through sweat" and describes induced sweating as a potential way to eliminate them.Source 1 · Cross-sectional studyBlood, Urine, and Sweat (BUS) Study: Monitoring and Elimination of Bioaccumulated Toxic ElementsGenuis SJ, Birkholz D, Rodushkin I, et al.. Archives of Environmental Contamination and Toxicology, 2011.Read the paper ↗PubMed ↗ We couldn't get access to the paper's own tables.

A 2012 systematic review reprinted the study's values. Its tables give mean lead of 31 µg/L in sweat and 1.8 µg/L in urine. For mercury the two figures were 0.86 and 0.65 µg/L.Source 2 · Systematic reviewArsenic, Cadmium, Lead, and Mercury in Sweat: A Systematic ReviewSears ME, Kerr KJ, Bray RI. Journal of Environmental and Public Health, 2012.Read the paper ↗PubMed ↗ The same tables print an arsenic mean of 3.1 µg/L next to a range of 3.7–22, and a mean can't fall outside its own range. A 2023 paper lists different arsenic and cadmium values for the study.Source 2 · Systematic reviewArsenic, Cadmium, Lead, and Mercury in Sweat: A Systematic ReviewSears ME, Kerr KJ, Bray RI. Journal of Environmental and Public Health, 2012.Read the paper ↗PubMed ↗Source 3 · Case seriesEffect of water filtration infrared-A (wIRA) sauna on inorganic ions excreted through sweat from the human bodyCho KH, Jung SH, Choi MS, et al.. Environmental Science and Pollution Research, 2023.Read the paper ↗PubMed ↗

The project's 2012 paper on the plastics chemical BPA also drew on 20 participants, and it describes the collection in full. Each person gathered at least 100 mL of sweat from anywhere on the body, either by holding a glass jar to prewashed skin or by scraping sweat off with a stainless-steel spatula. The method didn't say how long people should sweat before collecting.Source 4 · Cross-sectional studyHuman Excretion of Bisphenol A: Blood, Urine, and Sweat (BUS) StudyGenuis SJ, Beesoon S, Birkholz D, et al.. Journal of Environmental and Public Health, 2012.Read the paper ↗PubMed ↗

Methods like these also collect whatever was already on the skin. In one study, scraped sweat carried 4 to 10 times more lipid (fat) than clean sweat.Source 5 · Clinical trialFree fatty acids and sterols in human eccrine sweatTakemura T, Wertz P, Sato K. British Journal of Dermatology, 1989.Read the paper ↗PubMed ↗ When 24 people had their sweat caught in arm bags in a hot chamber, lead in their sweat averaged about a quarter of the level in their urine.Source 6 · Clinical trialLead in sweat and its relationship to salivary and urinary levels in normal healthy subjects1Omokhodion F, Crockford G. The Science of The Total Environment, 1991.Read the paper ↗PubMed ↗

The study can't tell you these things

  • Each person collected one sweat sample themselves. The study didn't control how long they had sweated or which part of the body the sweat came from.
  • One sample of each fluid gives a concentration. It can't show how much metal leaves the body through sweat or urine over a whole day.
  • Some participants came from the lead author's clinical practice, and the group was small.
  • Its numbers reach readers through other papers' tables, and those contain errors. One prints an arsenic mean outside its own range.Source 2 · Systematic reviewArsenic, Cadmium, Lead, and Mercury in Sweat: A Systematic ReviewSears ME, Kerr KJ, Bray RI. Journal of Environmental and Public Health, 2012.Read the paper ↗PubMed ↗
  • It didn't look at anyone's health or at how much metal stays stored in the body.

People quote it like this

A 2022 crossover study and a 2023 study of an infrared capsule both cite it as evidence that metals leave the body preferentially through sweat.Source 7 · Crossover trialExcretion of Ni, Pb, Cu, As, and Hg in Sweat under Two Sweating ConditionsKuan WH, Chen YL, Liu CL. International Journal of Environmental Research and Public Health, 2022.Read the paper ↗PubMed ↗Source 3 · Case seriesEffect of water filtration infrared-A (wIRA) sauna on inorganic ions excreted through sweat from the human bodyCho KH, Jung SH, Choi MS, et al.. Environmental Science and Pollution Research, 2023.Read the paper ↗PubMed ↗ When the 2022 study collected its own sweat under controlled conditions in a 45°C sauna cabinet, the samples held 4.9 µg/L of lead.Source 7 · Crossover trialExcretion of Ni, Pb, Cu, As, and Hg in Sweat under Two Sweating ConditionsKuan WH, Chen YL, Liu CL. International Journal of Environmental Research and Public Health, 2022.Read the paper ↗PubMed ↗

We cited these sources

  1. 01Genuis SJ, Birkholz D, Rodushkin I, Beesoon S. Blood, Urine, and Sweat (BUS) Study: Monitoring and Elimination of Bioaccumulated Toxic Elements. Archives of Environmental Contamination and Toxicology. 2011;61(2):344-357. doi:10.1007/s00244-010-9611-5 PMID 21057782
  2. 02Sears 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 PMID 22505948
  3. 03Cho KH, Jung SH, Choi MS, Jung YJ, Lee CG, Choi NC. Effect of water filtration infrared-A (wIRA) sauna on inorganic ions excreted through sweat from the human body. Environmental Science and Pollution Research. 2023;30(7):18260-18267. doi:10.1007/s11356-022-23437-3 PMID 36207634
  4. 04Genuis SJ, Beesoon S, Birkholz D, Lobo RA. Human Excretion of Bisphenol A: Blood, Urine, and Sweat (BUS) Study. Journal of Environmental and Public Health. 2012;2012:185731. doi:10.1155/2012/185731 PMID 22253637
  5. 05Takemura T, Wertz P, Sato K. Free fatty acids and sterols in human eccrine sweat. British Journal of Dermatology. 1989;120(1):43-47. doi:10.1111/j.1365-2133.1989.tb07764.x PMID 2638916
  6. 06Omokhodion F, Crockford G. Lead in sweat and its relationship to salivary and urinary levels in normal healthy subjects1. The Science of The Total Environment. 1991;103(2–3):113-122. doi:10.1016/0048-9697(91)90137-4 PMID 1882227
  7. 07Kuan WH, Chen YL, Liu CL. Excretion of Ni, Pb, Cu, As, and Hg in Sweat under Two Sweating Conditions. International Journal of Environmental Research and Public Health. 2022;19(7):4323. doi:10.3390/ijerph19074323 PMID 35410004