A hot, dry room at 80–100°C. Frequent use is linked to fewer heart deaths in Finnish studies: the best long-term data on this shelf, but observational.
A traditional sauna heats the air and stones to about 80–100°C (176–212°F) at low humidity; throwing water on the stones briefly raises the steam. The category covers indoor cabins and outdoor barrels and cubes, with electric or wood-fired heaters.
A session works a bit like light exercise for your circulation: heart rate climbs to roughly 100–150 beats per minute, blood vessels widen, and blood pressure dips afterward. The long-term evidence comes from Finland, where sauna use is ordinary rather than a wellness trend.
In 2,315 Finnish men followed for about 20 years, using a sauna 4–7 times a week was linked to about 40% lower all-cause mortality than once a week, and the same research group has linked frequent use to less stroke, hypertension and dementia. Small randomized trials of repeated heat show better artery function and blood pressure, which fits. But these are observational data, mostly from one research group in one region, using hot traditional saunas (~79°C, ~14-minute sessions); no trial shows sauna use itself extends life.
In 2,315 middle-aged Finnish men followed for a median of about 20 years, sauna use 4–7 times a week was associated with lower sudden cardiac death, fatal heart disease and all-cause mortality than once a week, after adjustment for cardiovascular risk factors.
In 1,628 Finnish men and women aged 53–74 followed for a median of 14.9 years, 4–7 sauna sessions a week was associated with a 61% lower risk of stroke than one session (HR 0.39), after adjusting for risk factors, physical activity and socioeconomic status.
In 20 young sedentary adults, 8 weeks of repeated hot-water immersion (4–5 times a week, raising core temperature to at least 38.5°C) improved artery dilation, arterial stiffness and mean blood pressure (83 to 78 mmHg) compared with thermoneutral immersion.
Reviewing deaths that occurred in saunas in Finland from 1990 to 2002, the annual rate was under 2 per 100,000 people; half of those who died were under the influence of alcohol.