What do the heat and the cold actually do?
Heat raises core temperature and loads the heart and circulation the way moderate exercise does. Cold reverses it within seconds. Here is what is known about that, and what is not.
In the heat, blood moves to the skin, heart rate climbs into a range comparable with moderate exercise, and you sweat heavily. Do it often enough and the body adapts to heat the way it adapts to a training load.
In cold water the opposite happens almost instantly. Vessels close, breathing catches, and the body releases a large amount of noradrenaline. That is the source of the clean, wide-awake state people describe afterwards, and it is why the cold is not a flourish at the end of the session but half of the mechanism.
Most of the research that exists is Finnish and concerns their dry sauna. The largest long-running study followed 1,688 Finnish adults for a median of fifteen years and found that people bathing four to seven times a week had markedly lower cardiovascular mortality than those going once a week — a hazard ratio of 0.23 after adjustment for risk factors. That number is worth reading carefully. It is observational, not a trial: people who sit in a sauna five times a week may differ from those who do not in ways no statistical adjustment catches. The authors state plainly that results from Finnish sauna cannot be transferred directly to other kinds of steam room.
So the honest position is this. Heat and cold do real and measurable things to the body, and people have organised their week around them for a thousand years for reasons that were never mystical. What we will not tell you is that two hours on a boat will fix anything in particular. Come for what the ritual does in the room and in the hours after it, and hold everything beyond that as an open question.
Updated 2026-09-02