“Sauna switches on heat shock proteins that slow aging.”

The research found this

The sauna evidence rests on one study. At the University of Iowa, 25 young adults sat in random order for 30 minutes in a sauna-style chamber at 73°C on one day and at 26.1°C on another.1Source 1 · 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 ↗ In the 13 who gave blood, extracellular heat shock protein 72 rose 48.7% on average after the heat. The variation between people (±53.9%) was larger than the average rise.

Hot-water studies point in different directions. In people with type 2 diabetes, blood HSP70 measured 402 pg/mL when an hour in 40°C water came before a glucose test, against 203 pg/mL without heat.2Source 2 · Crossover trialTiming of acute passive heating on glucose tolerance and blood pressure in people with type 2 diabetes: a randomized, balanced crossover, control trialJames TJ, Corbett J, Cummings M, et al.. Journal of Applied Physiology, 2021.Read the paper ↗PubMed ↗ In another group with diabetes, an hour of hot water that held core temperature at 38.5°C or more changed neither blood nor cell levels.3Source 3 · Crossover trialAcute effect of passive heat exposure on markers of cardiometabolic function in adults with type 2 diabetes mellitusBehzadi P, Ravanelli N, Gravel H, et al.. Journal of Applied Physiology, 2022.Read the paper ↗PubMed ↗ Overweight men who spent an hour in 39°C water showed no change in the protein inside their immune cells, and after two weeks of sessions their blood level had fallen 17%.4Source 4 · Crossover trialAcute and chronic effects of hot water immersion on inflammation and metabolism in sedentary, overweight adultsHoekstra SP, Bishop NC, Faulkner SH, et al.. Journal of Applied Physiology, 2018.Read the paper ↗PubMed ↗

Pooled data settle on no change. A 2025 meta-analysis of 51 controlled studies of heating without exercise found heat shock proteins unchanged after single or repeated sessions.5Source 5 · Meta-analysisHeat thermotherapy to improve cardiovascular function and cardiometabolic health: A systematic review and meta‐analysisPrice BS, Lucas SJE, Akerman AP, et al.. Experimental Physiology, 2025.Read the paper ↗PubMed ↗ Heat applied straight to muscle does raise them there: two hours a day of shortwave diathermy raised muscle HSP70 by 45% after six days in one study and by 25% during 10 days of immobilization in another.6Source 6 · Clinical trialRepeated exposure to heat stress induces mitochondrial adaptation in human skeletal muscleHafen PS, Preece CN, Sorensen JR, et al.. Journal of Applied Physiology, 2018.Read the paper ↗PubMed ↗7Source 7 · Clinical trialDaily heat treatment maintains mitochondrial function and attenuates atrophy in human skeletal muscle subjected to immobilizationHafen PS, Abbott K, Bowden J, et al.. Journal of Applied Physiology, 2019.Read the paper ↗PubMed ↗

Heat also switches on the genes. In a depression trial, blood drawn 30 minutes after whole-body hyperthermia showed more activity in several heat shock protein gene families than blood drawn after a sham.8Source 8 · Clinical trialWhole-blood transcriptomic response to whole-body hyperthermia in participants with major depressive disorderAkonom TN, Allen MA, Begay TK, et al.. Brain, Behavior, & Immunity - Health, 2026.Read the paper ↗PubMed ↗ The aging half of the claim comes from animal research, and no study has followed people to see whether heat shock proteins from a sauna change how they age.