Sauna and ice swimming: when not to go

Sauna and winter swimming carry risks that depend on health, alcohol use and the conditions at the bathing place. Findings about sauna bathing cannot by themselves establish the safety of cold-water immersion. Here is what the cited sources say, and where their evidence stops.

Three situations get a flat no from the sources: alcohol, fever and going alone. Four more,

asked just as often, have no research behind them at all. Here is each one, and what the

Alcohol. A peer-reviewed review says it outright: drinking during a

sauna raises the risk of low blood pressure, arrhythmia and sudden death, and should be

avoided. Suomen Latu says the same about the water.

Illness, especially a fever. Skip both. The named risk is not

discomfort. It is that exertion may increase the danger of a complication such as viral

Going in alone. Suomen Latu’s safety list opens with it, and the

reason is a reflex you cannot override by willpower during the first minute.

Blood-pressure medication is a caution, not a ban, and the pressure drop

comes after the sauna rather than during it.

Periods, a heavy meal, poor sleep, a hard workout just before. Not one

source we opened addresses any of them. That is not the same as safe.

Drinking during a sauna raises the risk of low blood pressure, arrhythmia and sudden death,

and should be avoided. That is the conclusion of a peer-reviewed review of sauna benefits and

risks, and it is unusually direct. Suomen Latu is just as short about the water: do not swim

while ill or under the influence of alcohol, and never alone.

Ten healthy men were measured sober and after heavy drinking. The sauna alone left systolic blood pressure at baseline. The sauna combined with heavy drinking dropped it from 136 to 113 mmHg. Ventricular extra beats did not increase in either condition, and they were the only arrhythmia this experiment counted. The authors’ own sentence is about blood pressure, not collapse. These blood-pressure measurements do not establish whether anyone fainted. An outcome that was not measured cannot be treated as an outcome that did not occur.

Death in a sauna is rare. In Finnish forensic data from 1990 to 2002 it ran to fewer than two

cases per 100,000 inhabitants per year, and half of those cases were under the influence of

alcohol. The researchers’ own prevention advice has two halves, and the second one gets

forgotten: less alcohol, and do not leave an intoxicated bather alone.

Drownings have their own Finnish dataset: 1,697 accidental drownings of people aged 15 and

over between 2000 and 2009, all forensically tested. Alcohol-positive cases, defined there as

a blood alcohol concentration of at least 0.5 per mille, made up 61.8 per cent of

non-boating drownings and 65.0 per cent of boating ones. The figure says how many drowning

victims had alcohol in their blood. It does not say how many drinkers drown.

And a hangover? The useful question is not how you feel but whether there is still alcohol in

your blood. If there is, everything above applies and the hangover changes none of it. If

there is not, we found no study at all on hangovers combined with a sauna or an ice hole, and

The beer straight after the steam is a smaller question with a real answer. In a rehydration

experiment where the fluid loss had been induced by exercise, a 4 per cent drink slowed the

recovery of blood and plasma volume, while drinks at 2 per cent or below did not differ from

the alcohol-free one. Ordinary beer is 4 per cent or stronger, which is the range where

recovery slowed. Two limits: the dehydration came from exercise rather than heat, and none of

Anyone who has caught a cold should avoid the sauna, particularly with a fever. The

reasoning behind that guidance from Terveyskirjasto, the Finnish Medical Society’s

public health library, is the part worth keeping: a feverish body does not need more heat or

more load, and exertion may increase the danger of complications such as viral myocarditis.