Do saunas and cold plunges help you get sick less?
"I haven't had a cold since I started" is one of the most common things sauna and plunge owners say. Here's what the research actually shows about heat, cold and immunity, which claims hold up, and how to use both sensibly during cold and flu season.
Sauna and respiratory infections
The best-known study is an Austrian trial from 1990: 50 volunteers were split into sauna and no-sauna groups for six months; the sauna group had about half as many colds, with the difference appearing after the third month. It's small and old but randomized. A later Finnish cohort found frequent sauna users had about 40% lower risk of pneumonia and lower rates of respiratory disease overall, with the usual observational caveats. A Dutch trial found regular sauna users reported fewer sick days.
Proposed mechanisms: a sauna session raises white blood cell counts temporarily, mimics a mild fever (which is part of how the body fights viruses), and improves sleep and lowers stress, both of which measurably affect immune function. Warm, humid air may also help clear mucus from airways, which is why a traditional sauna feels good when you're congested.
Cold water and immunity
A large Dutch study randomized 3,000 people to end their showers with 30-90 seconds of cold for a month. Sick days dropped about 29%, though the number of people who reported being ill didn't change; they felt well enough to work through it. Winter swimmers show higher counts of some immune cells and report fewer upper respiratory infections in surveys. As with sauna, the evidence is encouraging and modest, and the people who choose cold swimming are not a random sample.
What to make of it
- Regular heat and cold exposure probably reduce how often you catch mild respiratory infections, or how hard they hit, by a modest amount.
- Neither is a substitute for vaccines, sleep, hand washing or not being around sick people.
- Most of the reported effect may run through sleep and stress rather than any direct "immune boost."
- The "boosting your immune system" framing is marketing. The immune system isn't a dial; it's a balance, and a well-regulated one is the goal.
Using them when you're already sick
| Situation | Sauna / cold | Verdict |
|---|---|---|
| Stuffy nose, mild cold, no fever | A gentle sauna (cooler, shorter) often feels good and may help congestion. Hydrate. Skip the plunge | Fine for most |
| Fever | No. Your body is already running hot; adding heat is a load it doesn't need | Rest instead |
| Flu, body aches, exhaustion | No sauna, no cold. Both are stressors; your body needs the resources | Wait until fever-free 24-48 hours |
| Lingering cough after a cold | Warm, humid traditional sauna can soothe; stop if it triggers coughing fits | Gentle |
| Chest infection, pneumonia, COVID with breathing symptoms | No. See a doctor | Medical care |
| Recovering, feeling 80% | Short, cool sessions to ease back in. Not a contrast circuit yet | Build back over a week |
A cold-season routine
- Sauna 3-5 times a week, 15-20 minutes, year round. The Austrian study's benefit took three months to appear; this isn't a quick fix.
- End showers cold for 30-60 seconds, or plunge in the morning 3-5 days a week.
- Protect sleep, which both habits help with and which matters more than either for staying well.
- Don't push through illness with heat or cold. Rest is the therapy then.
Related: the science of saunas, cold plunge benefits and risks, and the contrast circuit.
General education, not medical advice. Talk to your doctor before starting heat or cold therapy if you are pregnant or have a heart, blood pressure or neurological condition.