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Sauna Hype

The claim

“A sauna sweats microplastics out of your body.”

Hot air. No study has found microplastics in sweat or tested whether a sauna lowers the amount in blood or semen. The idea spread from Bryan Johnson's self-tests, and Johnson himself wrote that he can't prove the sauna caused his drop and that the particles are too big to sweat out.

Updated Sep 24, 2026

Nothing solid supports it, or the best evidence runs against it.

People say it in places like these

  • News coverage

    A biohacker got rid of 85% of the microplastics in his semen with a daily sauna.

    See an example ↗

  • Sauna sellers

    Regular sauna sessions help flush microplastics out of your body.

  • Bryan Johnson on X

    Daily sauna was the change most likely behind an 85% drop in microplastics in his ejaculate.

    See an example ↗

The research found this

Microplastics are plastic fragments smaller than 5 mm. The blood tests sold to consumers take a finger-prick spot of blood, stain it with a dye that sticks to plastic and count the glowing particles under a microscope.Source 1 · Web pageHow does the test work?Blueprint. Blueprint help centre, 2026.Read the page ↗ A 2026 pilot study used one of these kits on 29 people. Its authors called the results semi-quantitative and noted that they ran no blank samples to check for contamination.Source 2 · Cross-sectional studyThe Association of Microplastics in Peripheral Blood and Pulmonary Disease: A Pilot StudyHelgeson SA, Alaws H, Ibrahim MI, et al.. Journal of Xenobiotics, 2026.Read the paper ↗PubMed ↗

Research labs struggle to measure plastic in the body too. A 2025 study found that ordinary fats in blood can read as polyethylene and PVC in one widely used method, and its authors judged that method unsuitable for those plastics in human samples.Source 3 · DatasetAssessing the Efficacy of Pyrolysis-Gas Chromatography-Mass Spectrometry for Nanoplastic and Microplastic Analysis in Human BloodRauert C, Charlton N, Bagley A, et al.. Environmental Science & Technology, 2025.Read the paper ↗PubMed ↗ Several of the best-known findings of plastic throughout the human body now face formal challenges.Source 4 · News report'A bombshell': doubt cast on discovery of microplastics throughout human bodyCarrington D. The Guardian, January 13, 2026, 2026.Read the page ↗

No study has looked for plastic particles in human sweat. The consumer kit counts particles between 1 and 70 thousandths of a millimeter across, and Johnson himself now says they're too big to leave the body that way.Source 1 · Web pageHow does the test work?Blueprint. Blueprint help centre, 2026.Read the page ↗Source 5 · Web pagePost reporting no microplastics in his semenJohnson B. Post on X, May 7, 2026, 2026.Read the page ↗

The one treatment with published numbers is plasma exchange, which filters the blood through plastic tubing. In 114 patients, particle counts fell only in people who started high, because the tubing shed particles of its own.Source 6 · Case seriesCan Plasma Exchange Be Used to Lower the Circulating Burden of Microplastics in Human Patients?Weinstein R, Yuksel ZS, Anderson C, et al.. Journal of Clinical Apheresis, 2026.Read the paper ↗PubMed ↗

The dial reads 90°H for four reasons

How the reading adds up

25 + 18 + 25 + 22 = 90°H

  1. EvidenceWhat kind of human evidence exists?

    25/25

    The only data come from one person's tests, with one sample before each change and one after, on a consumer kit that hasn't published validation data.Source 7 · Web pagePost saying he eliminated 85% of microplastics from his ejaculateJohnson B. Post on X, October 21, 2025, 2025.Read the page ↗Source 2 · Cross-sectional studyThe Association of Microplastics in Peripheral Blood and Pulmonary Disease: A Pilot StudyHelgeson SA, Alaws H, Ibrahim MI, et al.. Journal of Xenobiotics, 2026.Read the paper ↗PubMed ↗

  2. ConsistencyHave other studies found the same thing?

    18/25

    Bryan Johnson ran the best-known tests, and he later wrote that he couldn't prove the sauna caused the drop and that the particles are too big to sweat out.Source 5 · Web pagePost reporting no microplastics in his semenJohnson B. Post on X, May 7, 2026, 2026.Read the page ↗

  3. MagnitudeDoes the claim match the size of the effect?

    25/25

    The 85% figure that headlines repeated compares two single semen samples taken eight months apart, and the matching blood result was one particle multiplied by ten.Source 7 · Web pagePost saying he eliminated 85% of microplastics from his ejaculateJohnson B. Post on X, October 21, 2025, 2025.Read the page ↗Source 8 · Web pagePost saying he cut the microplastics in his blood by 93%Johnson B. Post on X, June 23, 2025, 2025.Read the page ↗

  4. DoseDoes the studied dose match how people use it?

    22/25

    His routine was an ordinary one, 20 minutes a day at 93°C. No study has tested any sauna routine against microplastics in the body.Source 9 · Web pagePost in the same thread giving his sauna protocolJohnson B. Post on X, May 7, 2025, 2025.Read the page ↗

The claim drifts from the data here

Johnson's blood went from 70 particles per milliliter in October 2024 to 10 in May 2025. The lab counted seven particles and then one, and multiplied each count by ten because it assumes every sample holds a tenth of a milliliter.Source 8 · Web pagePost saying he cut the microplastics in his blood by 93%Johnson B. Post on X, June 23, 2025, 2025.Read the page ↗ His first plasma exchange came days after the October test, and the May report may cover blood drawn before his first sauna session.Source 10 · Web pagePost on his first total plasma exchangeJohnson B. Post on X, October 14, 2024, 2024.Read the page ↗Source 11 · Brand pageMicroplastics Test (product page)Blueprint. Blueprint store, 2026.Read the page ↗ Our calendar of his results lays out the dates.

His semen readings fell from 165 to 20 and then to zero over 17 months. In that stretch he also switched to filtered water and cleared plastic out of his kitchen.Source 7 · Web pagePost saying he eliminated 85% of microplastics from his ejaculateJohnson B. Post on X, October 21, 2025, 2025.Read the page ↗Source 5 · Web pagePost reporting no microplastics in his semenJohnson B. Post on X, May 7, 2026, 2026.Read the page ↗ When the April 2026 test came back at zero, he wrote that he couldn't prove which change did it.

Put it to use

Use the sauna for the heat. If you want to take in less plastic, start with the sources researchers have measured: microwaving food in plastic containers and chopping on plastic cutting boards both shed particles into food.Source 12 · DatasetAssessing the Release of Microplastics and Nanoplastics from Plastic Containers and Reusable Food Pouches: Implications for Human HealthHussain KA, Romanova S, Okur I, et al.. Environmental Science & Technology, 2023.Read the paper ↗PubMed ↗Source 13 · DatasetCutting Boards: An Overlooked Source of Microplastics in Human Food?Yadav H, Khan MRH, Quadir M, et al.. Environmental Science & Technology, 2023.Read the paper ↗PubMed ↗ Nobody has shown how much those swaps change what ends up in your blood.

From our sister magazine

Sauna Monthly explains how to build a daily sauna habit

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Finns made the daily sauna a habit

Sauna Monthly explains how to make four sessions a week feel automatic.

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Sauna Monthly turns the Finnish research into a buying brief

The piece walks through the long Finnish study and what it means for a home sauna.

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People also ask

Did Bryan Johnson sweat out microplastics?

He doesn't claim to know. His blood and semen counts fell while he was also having plasma exchange, filtering his water and removing plastic from his home, and in May 2026 he wrote that he couldn't prove cause and that the particles are too big to sweat out.Source 5 · Web pagePost reporting no microplastics in his semenJohnson B. Post on X, May 7, 2026, 2026.Read the page ↗

Can you sweat out microplastics?

No study has found microplastic particles in human sweat. Bryan Johnson's self-tests made the idea popular, and he says the particles are too big to leave through sweat.Source 5 · Web pagePost reporting no microplastics in his semenJohnson B. Post on X, May 7, 2026, 2026.Read the page ↗

How accurate are at-home microplastics blood tests?

The companies haven't published validation data. A pilot study that used one kit ran no contamination blanks and described its results as semi-quantitative.Source 2 · Cross-sectional studyThe Association of Microplastics in Peripheral Blood and Pulmonary Disease: A Pilot StudyHelgeson SA, Alaws H, Ibrahim MI, et al.. Journal of Xenobiotics, 2026.Read the paper ↗PubMed ↗

Check these claims next

68°H

Stretched

Heat

“You can sweat out toxins in a sauna.”

Sweat carries traces of metals and chemicals, and the studies that report large amounts relied on sweat people scraped off their own skin. When researchers collected sweat carefully, a session's worth held a small fraction of what the kidneys clear in a day.

96°H

Hot air

Heat

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

No study backs these percentages, and measured sweat is at least 99% water. An infrared sauna seller was already crediting them to an unnamed American study in 2002.

30°H

Likely

Heat

“Regular sauna use lowers your sperm count.”

In a small Italian study, 10 men took two 15-minute sessions a week at 80–90°C for three months, and their sperm count and motility (how well sperm swim) dropped. Every change the researchers measured had reversed six months after the men stopped.

We cited these sources

  1. 01Blueprint. How does the test work?. Blueprint help centre. 2026. Accessed Sep 24, 2026.
  2. 02Helgeson SA, Alaws H, Ibrahim MI, Lee AS, Vlecken DHW, Baig HZ. The Association of Microplastics in Peripheral Blood and Pulmonary Disease: A Pilot Study. Journal of Xenobiotics. 2026;16(3). doi:10.3390/jox16030072 PMID 42201067
  3. 03Rauert C, Charlton N, Bagley A, Dunlop SA, Symeonides C, Thomas KV. Assessing the Efficacy of Pyrolysis-Gas Chromatography-Mass Spectrometry for Nanoplastic and Microplastic Analysis in Human Blood. Environmental Science & Technology. 2025;59(4):1984-1994. doi:10.1021/acs.est.4c12599 PMID 39851066
  4. 04Carrington D. 'A bombshell': doubt cast on discovery of microplastics throughout human body. The Guardian, January 13, 2026. 2026. Accessed Sep 24, 2026.
  5. 05Johnson B. Post reporting no microplastics in his semen. Post on X, May 7, 2026. 2026. Accessed Sep 24, 2026.
  6. 06Weinstein R, Yuksel ZS, Anderson C, Grant D, Milius P, Waldron K, et al.. Can Plasma Exchange Be Used to Lower the Circulating Burden of Microplastics in Human Patients?. Journal of Clinical Apheresis. 2026;41(3):e70135. doi:10.1002/jca.70135 PMID 42169439
  7. 07Johnson B. Post saying he eliminated 85% of microplastics from his ejaculate. Post on X, October 21, 2025. 2025. Accessed Sep 24, 2026.
  8. 08Johnson B. Post saying he cut the microplastics in his blood by 93%. Post on X, June 23, 2025. 2025. Accessed Sep 24, 2026.
  9. 09Johnson B. Post in the same thread giving his sauna protocol. Post on X, May 7, 2025. 2025. Accessed Sep 24, 2026.
  10. 10Johnson B. Post on his first total plasma exchange. Post on X, October 14, 2024. 2024. Accessed Sep 24, 2026.
  11. 11Blueprint. Microplastics Test (product page). Blueprint store. 2026. Accessed Sep 24, 2026.
  12. 12Hussain KA, Romanova S, Okur I, Zhang D, Kuebler J, Huang X, et al.. Assessing the Release of Microplastics and Nanoplastics from Plastic Containers and Reusable Food Pouches: Implications for Human Health. Environmental Science & Technology. 2023;57(26):9782-9792. doi:10.1021/acs.est.3c01942 PMID 37343248
  13. 13Yadav H, Khan MRH, Quadir M, Rusch KA, Mondal PP, Orr M, et al.. Cutting Boards: An Overlooked Source of Microplastics in Human Food?. Environmental Science & Technology. 2023;57(22):8225-8235. doi:10.1021/acs.est.3c00924 PMID 37220346