“Infrared sauna sweat is 20% toxins, where a normal sauna's is only 3%.”

The research found this

We could not find a scientific source for these percentages. The earliest version we traced is a 2002 page from an infrared sauna seller. It credited one study by American researchers and never named it. The numbers were still traveling in June 2021, when WMC Action News 5 published a syndicated "Best Life" segment from Ivanhoe Broadcast News that credited them to unnamed studies. A dental clinic's blog repeated them that October and cited only the news page.

Sweat is almost all water. A 2019 review of sweat physiology gives the usual concentrations of what's dissolved in it: 10–90 mmol/L each for sodium and chloride, 5–40 mmol/L for lactate, 4–12 mmol/L for urea and 2–8 mmol/L for potassium.1Source 1 · ReviewPhysiology of sweat gland function: The roles of sweating and sweat composition in human healthBaker LB. Temperature, 2019.Read the paper ↗PubMed ↗ Add up the top of every range and you get about 10 g per liter. That's roughly 1% of sweat by mass. Lead runs at about 4–12 µg/L, and that comes to around a millionth of a percent.

The one study that compared sweat from different sauna types found that levels of the plastics chemical BPA didn't differ. In that 20-person BUS study, 10 people collected sweat in an infrared sauna and 10 in a steam sauna or during exercise.2Source 2 · 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 ↗

The only head-to-head test of sweat volume found less sweat in the infrared cabin. Twenty adults lost 0.39 kg over 45 minutes of far-infrared heat and 0.66 kg over three 10-minute rounds in a traditional sauna.3Source 3 · Crossover trialComparison of thermoregulatory, cardiovascular, and immune responses to different passive heat therapy modalitiesAtencio JK, Reed EL, Wiedenfeld Needham K, et al.. American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, 2025.Read the paper ↗PubMed ↗ That difference could have come down to chance (P = 0.16).

The highest metal readings come from a Korean hospital's capsule heated by water-filtered near-infrared light (infrared-A). Researchers collected the sweat running off every part of the body in 22 visitors, and 21 of them had conditions such as diabetes or cancer. Their sweat held mercury at 29.9 µg/L, and the study had no comparison group.4Source 4 · 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 ↗ A controlled study measured 0.2 µg/L in sweat from a sauna cabinet.5Source 5 · 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 ↗