Sauna when sick: does it help a cold, and when is it a bad idea?

The question arrives every December, and the answer in circulation is a shrug dressed up as a benefit: “it might help, and it certainly can’t hurt.” Half of that is wrong, and the other half deserves a number. Here is what has actually been measured, and where the heat stops being a comfort and starts being a load your body is already carrying.

Is sauna good for a cold? What the trials actually found

There is exactly one randomised controlled trial that asked whether a sauna visit helps a cold, and it was built carefully. Pach and colleagues, Medical Journal of Australia, 2010: 157 adults with common cold symptoms, recruited across two winters, all sat in a hot sauna cabin wearing winter coats so nobody could tell which group they were in. Eighty breathed hot dry air through the intervention device; seventy-seven breathed air at room temperature. The outcome was a standard symptom score over the following days.

No significant difference in symptom severity or in how long the cold lasted. The one secondary finding that separated the groups was that fewer people in the hot-air group took cold medicine on day one, 3 percent against 15 percent, which is the kind of single result that needs a second trial before it means anything.

Two other lines of evidence get quoted on this question, and both are about something else:

Read across that table and the honest summary is short. Nothing shows a sauna treats a cold. Something thin suggests regular bathers may catch fewer respiratory infections, and the mechanism for that, if it is real, is not something you can cash in on the day you are already sick.

Does a sauna help with a cold’s symptoms, or just feel like it?

Both things can be true, and it matters which one you are paying for.

Warm air, especially humid warm air, thins nasal mucus for a while and makes a blocked nose feel open. A quiet, hot, dim room is a genuinely good place to be when you feel terrible. Neither of those is the cold getting shorter, and the trial above is what separates the two: people felt no worse and got no better faster.

The folk version, “sweat it out”, does not survive contact with where a cold actually lives. Rhinoviruses replicate in the cells lining the nose and upper airway, and they do it best a few degrees below core body temperature, which is part of why they favour the nose in the first place. A 175°F room heats the air you breathe and the skin you sit on; the tissue inside your nose stays close to its normal temperature because your blood supply keeps it there, and it never approaches anything that would inactivate a virus. Sweat, meanwhile, is water and salt leaving through your skin. There is no route by which a cold virus rides out with it.

So the comfort is real and the cure is not. That is a fine reason to take a short, cool round when you have a stuffy head and no fever. It is not a reason to push through one when you feel genuinely ill, and the next section is where that line sits.

When not to: fever is the line

A traditional sauna round at 170 to 190°F raises core temperature by roughly 1 to 2°C over a 30-minute laboratory session, per the 2018 Mayo Clinic Proceedings review by Laukkanen and colleagues that our how long to stay in a sauna guide leans on, and it pulls out a volume of sweat that spa guidance puts on the order of a pint per round and that we have not yet weighed. In a healthy, hydrated adult those are the point. In someone whose core temperature is already up and whose fluid is already down, they are the problem.

Do not go in if any of these is true:

• You have a fever or chills. Your thermostat is already set high. Adding a degree or two on top of it is heat load with no upside, and the cardiovascular work of shedding it is work a febrile body is already doing.
• You have been vomiting or have had diarrhoea. You are short of fluid before you sit down; a round takes more.
• You feel dizzy or light-headed standing up. That is the first exit signal on a well day. On a sick day it is a reason not to start.
• You have chest tightness, wheeze or shortness of breath. Hot dry air is not kind to irritated airways, and a small hot room is the wrong place to find out how yours react.
• You have taken a decongestant in the last few hours. Pseudoephedrine and phenylephrine raise heart rate and blood pressure, and heat does too. Ask a pharmacist before you combine them; some antihistamines also blunt sweating, which is the mechanism you are relying on to stay safe in there.
• You will be sharing the room. See the etiquette section below. This one is about other people, not you.

The signals that mean out, once you are in, are the same ones our sauna temperature guide lists for a well bather, and they arrive sooner when you are ill: dizziness, nausea, a heart rate that is racing rather than elevated, a headache that started in the room, and sweat that stops while your skin feels hot and dry. Any one of them, out, cool air, water, done for the day.

Sauna with a cold, if you are going anyway: how the numbers change

For a mild head cold with no fever, no dizziness and nobody else in the room, here is how we would change a normal session. These are our adjustments to the figures in the how long guide, not numbers from a trial, and the direction of every change is the same: less heat, less time, more water.

Two practical notes. A lower setpoint is faster to reach: the heat-up calculator will show you that the same room and heater reaches 150°F well before it reaches 175°F, so a sick-day round costs less warm-up and less electricity as well as less of you. And skip the contrast. The sauna or cold plunge first protocol is a cardiovascular workout by design; a cold is not the day for it.

Sauna for the flu, a sinus infection or a cough

Flu. No. Influenza almost always brings a fever, and everything in the section above applies at full strength. This is the illness the “sweat it out” advice is most often given for and the one where it does the most harm.

Sinus congestion. Warm humid air is the thing that feels good here, and a sauna is warm but dry. A hot shower, a steam room or a bowl of steam under a towel delivers the humidity at a fraction of the heat load. The Cochrane review above, six trials of heated humidified air, found no benefit on the cold itself, so treat all of these as comfort measures, and pick the one that costs your body least. The sauna versus steam room comparison has the temperatures and humidities side by side.

A cough. Hot dry air at 175°F irritates an airway that is already inflamed, and some people find a dry sauna sets off a coughing fit that a steam room does not. If you have wheeze or any tightness, it is on the do-not-go-in list. If it is a lingering post-cold tickle with no fever, a short cool round with a ladle of water on the stones for humidity is the gentlest version of a sauna there is.

Is it safe to use a sauna when someone else is sick? Shared saunas

The question the Finnish forum threads are really about is not physiology, it is manners, and the answer there is clear: a sauna is a small, closed, warm room in which people breathe hard, and nothing about the heat sterilises it. Respiratory viruses travel on droplets and aerosols, and a 175°F reading at the ceiling does nothing to the air a metre lower that a sick person has just exhaled.

At home, alone, a sauna with a cold is your business. In a gym, a club or a shared building sauna, stay out until you are well; the people on the next bench did not sign up for your cold, and the bench itself is a surface you will sweat on. If you share a home sauna with someone who is ill, the ordinary things apply: separate sessions, a wipe-down of the benches, the vent open, and the door left ajar to air the room afterwards.

Can regular sauna use prevent colds?

This is the version of the question where the evidence is at least pointed in a direction, and it is worth being exact about how far it goes.

Ernst’s 1990 trial followed 25 regular sauna bathers and 25 controls for six months and counted colds: 33 episodes against 46, 221 days of symptoms against 343, with the difference appearing mostly in the last three months, as if it took time to build. It is a small, unblinded study from one group, and it has not been repeated at a size that would settle it. The Finnish KIHD cohort, 2,210 men followed for a median of 25.6 years, found that men who bathed two to three times a week had about 31 percent fewer hospital pneumonia diagnoses than men who bathed once or less, and men at four or more sessions about 44 percent fewer, after adjusting for the obvious confounders. That is an association in one population; the men who sauna most in Finland differ from the men who sauna least in ways a statistical adjustment only partly reaches.

So: plausible, not proven, and entirely about the weeks before you get sick rather than the days after. If you want the version of sauna use that the evidence speaks to at all, it is the regular habit, at the ordinary numbers in the how long guide, on the days you are well. It is not the emergency session on the day you are not.

What we have not measured

Nothing on this page is a measurement of ours, and one of the figures that matters most on a sick day is one we already owe.

Every trial result above is quoted from its published abstract, with the design and the sample size stated so you can weigh it yourself, and we have run no trial. The 1 to 2°C core-temperature rise is the laboratory figure from the Laukkanen review, in well subjects, over 30 minutes; nobody has published the same curve in someone with a fever and we would not run that study. The “do not go in” list is guidance, not data.

The number we can produce and have not is sweat loss per round: one subject on a bathroom scale before and after a 20-minute session at 180°F, no water in between, named as owed in our how long guide. The pint figure in circulation is repeated far more often than it is measured, and on a day when you are already short of fluid it is the figure that decides how much water “double the water” means. The sauna calorie and sweat estimator gives you the arithmetic for your own weight and session until then. Our how we test page says the same about every figure on the site.