The studies
These are the studies behind the claims.
Each page says who took part and what the researchers found. It also lists the limits that tend to fall out of the headline.
Height shows how many people a study followed, on a log scale. Most of what gets said about heat and cold rests on the low dots.
Researchers put these people in the heat
Clinical trialExperimental Physiology · 2026
Forty-five minutes of infrared heat at 65°C raised core temperature by 1.4°C
- People
- 12 adults (6 women)
- Length
- One 45-minute session
Crossover trialExperimental Physiology · 2026
A 90-second lake dip between sauna rounds kept core temperature and heart rate lower
- People
- 16 adults (8 women)
- Length
- One session on each of two days
Randomized trialJournal of Applied Physiology · 2025
Thirty hot-water sessions left blood pressure unchanged in untreated hypertension
- People
- 41 adults
- Length
- 8–10 weeks
Meta-analysisAmerican Journal of Preventive Cardiology · 2025
Randomized trials of regular heat found few lasting changes in heart risk markers
- People
- 20 randomized trials
- Length
- 2–15 weeks per trial
Randomized trialGlobal Advances in Integrative Medicine and Health · 2025
Adding sauna-dome heat to talk therapy did no better than sham heat in a pilot trial
- People
- 30 adults with major depression
- Length
- Eight weeks
Meta-analysisExperimental Physiology · 2025
Passive heating lowered blood pressure a little across 51 studies and left heat shock proteins and CRP unchanged
- People
- Participants of 51 controlled studies
- Length
- Single sessions and repeated programs
Crossover trialAmerican Journal of Physiology-Regulatory, Integrative and Comparative Physiology · 2025
A traditional sauna warmed the body more than an infrared cabin, and a hot bath warmed it most
- People
- 20 adults (10 women)
- Length
- Three single sessions
Clinical trialJournal of Applied Physiology · 2025
Infrared heat warmed the muscle nearest the skin most and left core temperature unchanged
- People
- 10 adults (6 women)
- Length
- One 45-minute session
Crossover trialExperimental and Clinical Endocrinology & Diabetes · 2024
One infrared sauna session made blood sugar rise more after a glucose drink in type 2 diabetes
- People
- 12 adults with type 2 diabetes
- Length
- Two single sessions
Randomized trialJournal of Applied Physiology · 2023
Eight weeks of Finnish sauna left blood vessel health unchanged in heart patients
- People
- 41 adults (33 men, 8 women)
- Length
- 8 weeks
Randomized trialThe Journal of Clinical Psychiatry · 2023
Eight weeks of heated yoga eased depression more than a waitlist did
- People
- 65 adults analyzed (80 randomized)
- Length
- Eight weeks
Randomized trialAmerican Journal of Physiology-Regulatory, Integrative and Comparative Physiology · 2022
Adding a sauna after exercise lowered blood pressure more than exercise alone
- People
- 47 adults
- Length
- 8 weeks
Crossover trialResearch Quarterly for Exercise and Sport · 2022
Adding a sauna after cycling training gave no extra gain in hemoglobin mass or aerobic fitness
- People
- 13 men
- Length
- Two four-week blocks
Crossover trialPLOS ONE · 2021
Whole-body heating raised blood BDNF in ten men
- People
- 10 men
- Length
- Three single sessions
Cohort studyPreventive Medicine Reports · 2020
A second Finnish cohort found no dementia benefit in its most frequent sauna users
- People
- 13,994 men and women
- Length
- Up to 39 years (1973–2011)
Cohort studyHeart · 2020
Japanese adults who took a hot bath almost daily had less heart disease and stroke
- People
- 30,076 men and women
- Length
- 1990 to 2009
Clinical trialJournal of Applied Physiology · 2019
Daily deep heating slowed muscle loss in legs held still for 10 days
- People
- 23 healthy adults
- Length
- 10 days
Cross-sectional studyComplementary Therapies in Medicine · 2019
Most sauna users in an online survey said sauna helped their sleep
- People
- 482 sauna users
- Length
- One year of data collection
Cohort studyNeurology · 2018
Finnish adults who took the most saunas had fewer strokes over 15 years
- People
- 1,628 men and women
- Length
- Median 14.9 years
Cohort studyBMC Medicine · 2018
Frequent sauna use tracked fewer heart deaths in men and left the question open for women
- People
- 1,688 people (867 women, 821 men)
- Length
- Median 15.0 years
Cohort studyAnnals of Medicine · 2018
Fitness predicted Finnish men's survival more strongly than sauna use did
- People
- 2,277 men
- Length
- Median 26.1 years
Clinical trialJournal of Human Hypertension · 2018
Blood pressure and artery stiffness fell right after one 30-minute sauna
- People
- 102 adults
- Length
- One session
Cohort studyAge and Ageing · 2017
Kuopio men who took four to seven saunas a week had fewer dementia diagnoses
- People
- 2,315 men
- Length
- Median 20.7 years
Cohort studyEuropean Journal of Epidemiology · 2017
Frequent sauna bathers had fewer lung disease diagnoses until deaths were taken into account
- People
- 1,935 men
- Length
- Median 25.6 years
Crossover trialTemperature · 2017
An hour in hot water burned 61 more calories than rest, and an hour of cycling burned 556 more
- People
- 14 men
- Length
- Two single sessions
Randomized trialCirculation Journal · 2016
Waon therapy improved walking distance in heart failure and missed its main target
- People
- 149 patients
- Length
- 2 weeks (10 sessions)
Randomized trialJAMA Psychiatry · 2016
One session of whole-body heating eased depression more than a sham session did
- People
- 29 adults analyzed (34 randomized)
- Length
- Six weeks of follow-up after one session
Cohort studyJAMA Internal Medicine · 2015
Finnish men who took the most saunas had fewer deaths over twenty years
- People
- 2,315 men
- Length
- Median 20.7 years
Randomized trialThe Journal of Alternative and Complementary Medicine · 2015
Eight weeks of regular sauna lowered headache intensity by 1.27 points in a small randomized trial
- People
- 37 people with chronic tension-type headache
- Length
- Eight weeks
Clinical trialHuman Reproduction · 2013
Three months of twice-weekly saunas cut sperm counts in 10 men, and the drop reversed after they stopped
- People
- 10 men
- Length
- Three months of sauna and six months of follow-up
Meta-analysisPLoS ONE · 2013
Alternating hot and cold water beat rest for soreness and showed no edge over cold water
- People
- 18 trials, 356 people
- Length
- From under 6 hours to more than 96 hours after exercise
Crossover trialJournal of Athletic Training · 2012
Thirty minutes in a 73°C sauna room raised blood heat shock protein 72 by 48.7% on average
- People
- 25 young adults (blood from 13)
- Length
- One heat session and one control session
Cross-sectional studyArchives of Environmental Contamination and Toxicology · 2011
Twenty people collected their own sweat, and the authors reported more of several toxic metals in it than in urine
- People
- 20 adults
- Length
- One sample of each fluid per person
Case seriesJournal of Forensic Sciences · 2008
Half of the people who died in Finnish saunas over 13 years had been drinking
- People
- Finland's 5.2 million people
- Length
- 13 years of records, 1990–2002
Crossover trialJournal of Science and Medicine in Sport · 2007
Six runners ran 32% longer to exhaustion after three weeks of post-training saunas
- People
- 6 male runners
- Length
- Two three-week periods with a three-week washout
Cohort studyJAMA: The Journal of the American Medical Association · 1992
Hot tubs early in pregnancy were linked to neural tube defects, and the sauna estimate was not statistically significant
- People
- 23,491 pregnant women
- Length
- Early pregnancy to birth
Clinical trialAnnals of Medicine · 1990
Twenty-five regular sauna users caught fewer colds than 25 non-users over six months
- People
- 50 volunteers
- Length
- Six months
Clinical trialActa Physiologica Scandinavica · 1986
Two hours of sauna a day for a week sent growth hormone up 16-fold
- People
- 10 men and 7 women
- Length
- One week
Researchers put these people in cold water
Crossover trialScientific Reports · 2025
Five minutes in an ice bath more than doubled noradrenaline at either time of day
- People
- 12 adults (6 women, 6 men)
- Length
- Two sessions on separate days
Clinical trialPLOS One · 2025
Two to three minutes in water below 4°C lowered young men's testosterone by about 19%
- People
- 13 young men (12 analyzed)
- Length
- One session
Cross-sectional studyPhysiological Reports · 2025
Cold water on the face slowed teenagers' hearts by 68 beats a minute
- People
- 54 teenagers in the face test, 20 in the body test
- Length
- One session
Meta-analysisPLOS ONE · 2025
One cold-shower trial supplied 3,018 of the 3,177 people in a meta-analysis of cold water and health
- People
- 11 studies, 3,177 people
- Length
- Outcomes from the moment of immersion to 48 hours, plus one 90-day trial
Randomized trialComprehensive Psychoneuroendocrinology · 2024
Cold showers with Wim Hof breathing did no better for depressive symptoms than warm showers with slow breathing
- People
- 84 women
- Length
- Three weeks, with follow-up at three months
Meta-analysisEuropean Journal of Sport Science · 2023
Cold water after strength training trimmed strength gains across ten studies
- People
- 10 studies, 170 people
- Length
- Varied by study
Clinical trialBiology · 2023
People felt better after five minutes in 20°C water, and their brain networks showed stronger coupling
- People
- 33 adults
- Length
- One session
Randomized trialPsychosomatic Medicine · 2022
Wim Hof breathing dampened the response to endotoxin, and cold training helped only in combination
- People
- 88 men
- Length
- Training followed by a single endotoxin test day
Cross-sectional studyCell Reports Medicine · 2021
Danish winter swimmers burned more energy in the cold than men who avoided it
- People
- 7 winter swimmers and 8 controls
- Length
- Three lab days and a 24-hour sub-study
Clinical trialNature Communications · 2021
Ten days of milder cold without shivering left insulin sensitivity unchanged
- People
- 9 patients with type 2 diabetes
- Length
- 10 days
Randomized trialPLOS ONE · 2016
Dutch adults who finished their showers cold took fewer sick days off work
- People
- 3,018 adults
- Length
- 90 days
Clinical trialNature Medicine · 2015
Ten days of cold air raised insulin sensitivity 43% in eight men with type 2 diabetes
- People
- 8 patients with type 2 diabetes
- Length
- 10 days
Randomized trialThe Journal of Physiology · 2015
Men who sat in cold water after leg workouts gained less muscle and strength over 12 weeks
- People
- 21 men (24 enrolled)
- Length
- 12 weeks
Randomized trialProceedings of the National Academy of Sciences · 2014
Men trained by Wim Hof had a weaker inflammatory response to an injected toxin
- People
- 24 men tested (30 enrolled)
- Length
- Ten days of training and home practice, then one test day
Randomized trialJournal of Clinical Investigation · 2013
Two hours a day in 17°C air for six weeks took 0.7 kg of fat off young men
- People
- 51 men screened; 22 in the six-week trial
- Length
- 6 weeks
Systematic reviewCochrane Database of Systematic Reviews · 2012
Cold water after exercise eased muscle soreness across 17 small trials
- People
- 17 trials, 366 people
- Length
- Soreness followed for up to 96 hours
Clinical trialEuropean Journal of Applied Physiology · 2000
An hour in 14°C water raised plasma dopamine in young men by 250%
- People
- 10 young men
- Length
- One hour per immersion
Clinical trialEuropean Journal of Applied Physiology · 2000
Six short cold dips roughly halved the breathing surge of cold shock for at least seven months
- People
- 12 men
- Length
- 14 months