“Sauna heat kills cancer cells.”

The research found this

One study has tracked sauna habits against cancer. Researchers in Kuopio, Finland, asked 2,173 men aged 42–61 with no history of cancer about their sauna use and then followed them for a median of 24.3 years. In that time, 588 of them developed cancer.1Source 1 · Cohort studyFinnish sauna bathing does not increase or decrease the risk of cancer in men: A prospective cohort studyLaukkanen JA, Mäkikallio TH, Khan H, et al.. European Journal of Cancer, 2019.Read the paper ↗PubMed ↗ Compared with men who went once a week or less, men who went two or three times a week had a hazard ratio for any cancer of 0.92 (95% CI 0.76–1.11). Four or more sessions a week gave the same 0.92 (0.66–1.27). A hazard ratio of 1 would mean no difference, and both plausible ranges (the 95% CI figures) include 1.

An older Finnish study found no protection either. It followed 4,475 men for lung cancer from 1964 to 1979, and heavy smokers who took saunas more than once a week had a higher risk (relative risk 1.7).2Source 2 · Cohort studySauna, dust and migration as risk factors in lung cancer among smoking and non‐smoking males in FinlandTenkanen L, Hakulinen T, Hakama M, et al.. International Journal of Cancer, 1985.Read the paper ↗PubMed ↗

In cancer care, heat treatment is a hospital procedure called hyperthermia. Devices with multiple antennas raise tumor tissue to 40–43°C under temperature monitoring, and the heat is given alongside radiotherapy or chemotherapy.3Source 3 · ReviewHyperthermia in combined treatment of cancerWust P, Hildebrandt B, Sreenivasa G, et al.. The Lancet Oncology, 2002.Read the paper ↗PubMed ↗ In a late-stage (phase 3) randomized trial of 341 people with high-risk soft-tissue sarcoma, adding regional hyperthermia to chemotherapy lowered the risk of the tumor growing at its original site, or of death, by 42% (relative hazard 0.58). After two years, 76% of the hyperthermia group were alive with no tumor growth at the original site, against 61% on chemotherapy alone.4Source 4 · Randomized trialNeo-adjuvant chemotherapy alone or with regional hyperthermia for localised high-risk soft-tissue sarcoma: a randomised phase 3 multicentre studyIssels RD, Lindner LH, Verweij J, et al.. The Lancet Oncology, 2010.Read the paper ↗PubMed ↗

Whole-body hyperthermia heats the entire patient. "Extreme" protocols hold core temperature at 41.5–42.0°C for 60 minutes under general anesthesia.5Source 5 · ReviewCurrent status of radiant whole-body hyperthermia at temperatures >41.5°C and practical guidelines for the treatment of adults. The German ‘Interdisciplinary Working Group on Hyperthermia’Hildebrandt B, Hegewisch-Becker S, Kerner T, et al.. International Journal of Hyperthermia, 2005.Read the paper ↗PubMed ↗6Source 6 · Case seriesAnaesthesiological experiences with whole body hyperthermiaKerner T, Hildebrandt B, Ahlers O, et al.. International Journal of Hyperthermia, 2003.Read the paper ↗PubMed ↗ A 2019 review counted four treatment-related deaths among 350 patients in earlier-stage (phase 2) studies, and it found no phase 3 trials.7Source 7 · ReviewWhole-body hyperthermia in combination with systemic therapy in advanced solid malignanciesLassche G, Crezee J, Van Herpen C. Critical Reviews in Oncology/Hematology, 2019.Read the paper ↗PubMed ↗

A sauna works on a much smaller scale. In a study where the same volunteers tried both, three 10-minute rounds in a traditional sauna raised core temperature by 0.4°C, and 45 minutes in an infrared cabin left it where it started.8Source 8 · 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 ↗ Longer, continuous heat pushed it higher. Rectal temperature reached 38.50°C after 30 minutes at 73°C in one study, and an infrared cabin at 65°C took it to 38.7°C in 45 minutes in another.9Source 9 · Crossover trialHeat Stress and Cardiovascular, Hormonal, and Heat Shock Proteins in HumansIguchi M, Littmann AE, Chang SH, et al.. Journal of Athletic Training, 2012.Read the paper ↗PubMed ↗10Source 10 · Clinical trialFar‐infrared sauna exposure at 65°C elevates core temperatureJenkins EJ, Killick JA, Grimm SR, et al.. Experimental Physiology, 2026.Read the paper ↗PubMed ↗