Three months of twice-weekly saunas cut sperm counts in 10 men, and the drop reversed after they stopped
This 2013 Human Reproduction study from Padova, Italy, followed 10 men through three months of sauna and six months of recovery. It is the longest sauna experiment on sperm we found.
The paper
Seminal and molecular evidence that sauna exposure affects human spermatogenesis
Garolla A, Torino M, Sartini B, Cosci I, et al.. Human Reproduction, 2013;28(4):877-885.
See the study at a glance
- Design
- Uncontrolled before-and-after study
- People
- 10 men
- Who they were
- Ten healthy volunteers in Padova, Italy. All had normal semen.
- What they did
- Two 15-minute sessions a week in a Finnish sauna at 80–90°C for three months. The researchers checked semen quality and sex hormones at four points between the first session and six months after the last.
- How long
- Three months of sauna and six months of follow-up
These numbers came out of it
89 → 31
Sperm concentration fell from 89 to 31 million per milliliter over the three months. A 2018 review took these figures from the paper's tables.
58% → 36%
The share of moving (motile) sperm dropped from 58% to 36%. These figures also come from the 2018 review.
No change
Sex hormone levels didn't change significantly over the sauna course.
6 months
Every measured change had reversed within six months of the last session.
The researchers did this
Ten men with normal semen took two 15-minute sessions a week in a Finnish sauna at 80–90°C for three months.Source 1 · Clinical trialSeminal and molecular evidence that sauna exposure affects human spermatogenesisGarolla A, Torino M, Sartini B, et al.. Human Reproduction, 2013.Read the paper ↗PubMed ↗ The researchers measured semen quality and sex hormones at four points between the start of the course and six months after it ended. They also tested how well the sperm's DNA was packed and how active their heat-stress genes were.
By the end of the course, sperm count and motility were strongly impaired (P < 0.001). Sex hormones hadn't changed significantly.Source 1 · Clinical trialSeminal and molecular evidence that sauna exposure affects human spermatogenesisGarolla A, Torino M, Sartini B, et al.. Human Reproduction, 2013.Read the paper ↗PubMed ↗ The share of sperm with normal DNA packing (histone-to-protamine exchange) fell from 78.7% to 69.0%, and a score of how well the sperm's mitochondria worked dropped from 76.8 to 54.0. Genes that respond to heat stress and low oxygen, such as HSP70 and HIF-1α, became more active.
The paper's tables with the size of the drop are paywalled. A 2018 systematic review that extracted them reports sperm concentration falling from 89 to 31 million per milliliter. Motile sperm went from 58.0% to 36.1%.Source 2 · Systematic reviewClinical Effects of Regular Dry Sauna Bathing: A Systematic ReviewHussain J, Cohen M. Evidence-Based Complementary and Alternative Medicine, 2018.Read the paper ↗PubMed ↗
Six months after the last session, every change had reversed.Source 1 · Clinical trialSeminal and molecular evidence that sauna exposure affects human spermatogenesisGarolla A, Torino M, Sartini B, et al.. Human Reproduction, 2013.Read the paper ↗PubMed ↗ The abstract doesn't report where things stood at three months.
The study can't tell you these things
- It had no control group, so each man was compared only with himself before the course.
- All 10 men had normal semen to begin with, and the authors named that as the study's main limitation. The sample was also small.
- It measured sperm and molecular markers and collected no data on fertility or pregnancy.
- The size of the fall comes from a review that copied it out of paywalled tables. Other summaries call it a 50% decline or a drop to about a third.Source 3 · ReviewEndocrine effects of sauna bathHuhtaniemi IT, Laukkanen JA. Current Opinion in Endocrine and Metabolic Research, 2020.Read the paper ↗Source 4 · GuidanceSauna ja terveys [Sauna and health]Viinikka L. Lääkärikirja Duodecim, Terveyskirjasto, 2024.Read the paper ↗
People quote it like this
A 2018 review of 40 sauna studies singled it out as the only one that reported a harm.Source 2 · Systematic reviewClinical Effects of Regular Dry Sauna Bathing: A Systematic ReviewHussain J, Cohen M. Evidence-Based Complementary and Alternative Medicine, 2018.Read the paper ↗PubMed ↗ Retellings put the drop anywhere from a 50% decline to a fall to about a third, and the Finnish health library that cites it still tells potential fathers they don't need to avoid the sauna.Source 3 · ReviewEndocrine effects of sauna bathHuhtaniemi IT, Laukkanen JA. Current Opinion in Endocrine and Metabolic Research, 2020.Read the paper ↗Source 4 · GuidanceSauna ja terveys [Sauna and health]Viinikka L. Lääkärikirja Duodecim, Terveyskirjasto, 2024.Read the paper ↗
From our sister magazine
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We cited these sources
- 01Garolla A, Torino M, Sartini B, Cosci I, Patassini C, Carraro U, et al.. Seminal and molecular evidence that sauna exposure affects human spermatogenesis. Human Reproduction. 2013;28(4):877-885. doi:10.1093/humrep/det020 PMID 23411620
- 02Hussain J, Cohen M. Clinical Effects of Regular Dry Sauna Bathing: A Systematic Review. Evidence-Based Complementary and Alternative Medicine. 2018;2018:1857413. doi:10.1155/2018/1857413 PMID 29849692
- 03Huhtaniemi IT, Laukkanen JA. Endocrine effects of sauna bath. Current Opinion in Endocrine and Metabolic Research. 2020;11:15-20. doi:10.1016/j.coemr.2019.12.004
- 04Viinikka L. Sauna ja terveys [Sauna and health]. Lääkärikirja Duodecim, Terveyskirjasto. 2024.