Cold water and sauna

The habit

In Finland the sauna is a room in the flat, like the kitchen. In Denmark the winter-swimming clubs on the harbours have waiting lists. In Sweden the kallbadhus, the cold bath house on stilts over the sea, has had people going down the ladder in January for a hundred years. In Norway the lake after the ski is just what you do. None of it is a treatment. It is a way to end a day outside, to sleep well, and to sit with other people for an hour with nothing to do.

The order is the same everywhere: sauna, cold water, sauna, cold water, and you finish warm. The water part is the one that needs care, so it comes first here.

What cold water does in the first minutes

Put a body into water colder than about 15 degrees and it reacts before you have any say. You gasp. You breathe fast and cannot slow it. The heart rate and blood pressure jump. This is the cold-shock response, and it is at its strongest in the first thirty seconds. As the skin cools to the water temperature, which takes a minute or two, it fades, and a few minutes in it is largely gone.

The people who know this best are at the University of Portsmouth, whose Extreme Environments Laboratory has studied cold-water immersion for decades; their conclusion that most sudden deaths in cold water happen in the first minutes and are caused by cold shock rather than by hypothermia is what the British lifeboat service turned into the advice to stop, lie back and float until the breathing settles. A 2017 review from the same laboratory, published in Experimental Physiology, looked across the whole field and found that the evidence for the different claims made for cold-water immersion varies, and that some of it is no more than anecdote. A 2020 narrative review in the International Journal of Environmental Research and Public Health reached the same two-sided conclusion: regular, graded and adjusted cold-water swimming by healthy, experienced people appears to go well, and there is a risk of death for the unaccustomed, from the initial cold shock or from a steady loss of swimming ability and hypothermia.

That is all the science this chapter needs. The gasp is real and it is dangerous if you are out of your depth or alone. It passes. Everything in how the Nordics do this is built around those two facts.

How to start

Autumn is the easy way in. A Nordic lake is 15 or 16 degrees in early September and loses a degree or so a week, so if you start then you adapt as it cools and never meet the full shock on a single day. Starting in January is possible, but it is the hard way and needs a club.

The first time: a bathing ladder or a shallow, firm bank, a wool hat, neoprene shoes if the bottom is stony, and a friend watching. Walk in to the waist. Breathe out slowly, long exhalations, and let the gasp pass. Go to the shoulders. Count ten calm breaths. Come out. That is a session, and it is enough.

Afterwards, dry off and dress at once, warm layers and a hat, and walk about. You will feel colder ten or twenty minutes after you get out than you did in the water, as the cold blood from the arms and legs comes back to the core, so do not stand around in a towel talking. A warm drink helps; the sauna helps more.

Go two or three times a week. The gasp and the panic fade after a handful of short immersions, and that is the only thing that gets easier: the water does not get warmer and the cooling does not slow down. So the time in the water grows in small steps over weeks, to two, three, five minutes for a confident regular, and the rule about shivering never changes. Hard shivering means the body has lost the argument; get out before it starts.

In midwinter the clubs cut a hole in the ice, an avanto in Finnish, with a ladder and a hut beside it. Go to the ladder, never under the ice, never alone, and the rest is the same as September.

The sauna

A Finnish sauna is 70 to 90 degrees, dry, with water thrown on the stones for a burst of steam, the löyly. Sit for ten to fifteen minutes, as long as it is pleasant and no longer, then out: a shower, the lake, the snow, or just the air. Cool down properly, go back in, and repeat two or three times. Drink water between rounds. Finish with a cool-down and a rest rather than a last round of heat. The sauna is not a competition and the top bench is not a medal.

The research that gets quoted is from the University of Eastern Finland, whose Kuopio cohort followed about 2,300 middle-aged men for twenty years and found, in a 2015 paper in JAMA Internal Medicine, that the men who used the sauna four to seven times a week had fewer fatal cardiovascular events and deaths over that time than the men who went once a week. It is an association in one population of Finnish men, not proof that the sauna did it; men who sit in the sauna every day may differ from the others in many ways. It is a reason not to worry about the habit, not a reason to prescribe it.

After a hard session the order is sauna first, then water. Eat and drink something before you go in if the session was long; a sauna on an empty, dehydrated body after a 90 km ski race is not pleasant, and the heat can make you lightheaded. Sit lower if it does. Stand up slowly.

What the evidence does and does not say

In plain words. Cold shock is real and dangerous and well studied. Habituation is real: the shock lessens with repeated short exposure. The Finnish cohort shows that frequent sauna goes with a lower rate of certain deaths, without showing why. Beyond that, the claims made for cold water about immunity, mood, metabolism and faster recovery are the claims that the Portsmouth review found to be of varied strength, some of them at the level of anecdote. This site does not make them.

What we will say is what Nordic people say: the dip and the sauna feel good, they make the day outside complete, they get you to sleep, and they are a reason to meet. That is enough to build a habit on. It is also exactly what the Nordic way is about: simple things done consistently, without a promise attached.

The Nordic week

In summer the lake is at the end of every run. In autumn the dip gets shorter and the sauna longer. In winter it is the club on Saturday morning, the ice hole, the hut, and the coffee afterwards. If you want the swimming to become more than a dip, the open-water swimming page explains how the races work and what water temperatures they set wetsuit rules at, and the events pages list the winter-swimming events where a 25 metre swim in an ice hole is the whole race. Train outside all year has the clothing for the walk home.