Sauna and Your Immune System: Can It Fight Colds?

The most direct evidence comes from a small 1990 randomised trial (Ernst and colleagues, published in Annals of Medicine). Fifty adults were split into a group who used a sauna twice a week and a control group who did not, and colds were tracked over six months. In the first three months there was little difference, but in the second three months the sauna group caught significantly fewer colds. The takeaway is that any benefit built up over time with regular use, rather than appearing straight away.

The larger picture comes from Finland, where sauna use is near-universal. A long-term study following nearly 2,000 middle-aged men for around 25 years (Kunutsor and Laukkanen, European Journal of Epidemiology, 2017) found that men who used a sauna four to seven times a week had roughly a 41%% lower risk of pneumonia than those who went once a week. There was a clear dose-response pattern: more frequent sessions tracked with lower respiratory-infection risk. This is observational data, so it cannot prove the sauna itself was the cause, but the size and consistency of the effect are striking.

There are a few plausible ways sitting in the heat could nudge the immune system, though it is fair to say the mechanisms are still being worked out.

The most talked-about is heat-shock proteins (a family of protective proteins cells produce in response to stress such as heat, defined in more detail by this overview of heat-shock proteins). Raising your core temperature triggers their production, and they play a role in cellular repair and in how immune cells function.

A sauna also produces a short, controlled rise in core temperature - a mild, artificial version of a fever. Because fever is one of the body's own tools for fighting infection, the theory is that periodically mimicking it may keep parts of the immune response primed. Studies have also measured short-term rises in white blood cells, lymphocytes and neutrophils - the cells involved in fighting infection - in the period immediately after a sauna session. These changes are transient, but over months of regular use they may add up to the modest protective effect the trials hint at.

This is where common sense matters more than the research. If you have a mild head cold - a runny nose, a bit of congestion, no fever and you otherwise feel well - a gentle, shorter sauna session is unlikely to do harm, and some people find the warmth and steam temporarily eases a blocked nose. Keep it brief, keep well hydrated, and stop if you feel light-headed.

The key rule is to avoid the sauna entirely if you have a fever or feel genuinely unwell. A sauna already raises your heart rate and core temperature and causes fluid loss through sweating; stacking that on top of a fever puts extra strain on the heart and worsens dehydration at exactly the wrong time. The NHS advice for a common cold is rest, fluids and time - not heat stress. If you are unsure, or symptoms are more than a mild cold, sit it out.

Beyond an active fever or infection, the sauna is not right for everyone. Give it a miss, or check with a GP first, if you:

• Have a fever or an acute infection of any kind.
• Feel faint, dizzy or dehydrated.
• Have a heart condition, uncontrolled blood pressure, or are pregnant - see our guide to who should not use a sauna.
• Have been drinking alcohol, which compounds dehydration and cardiovascular strain.

For the wider picture on sauna use and the heart, see our guide to sauna and cardiovascular health.

The research offers a rough steer here. The benefits in both the cold trial and the Finnish pneumonia study showed up with regular, sustained use - twice a week in the trial, and four to seven times a week for the strongest effect in the cohort study. A single session before a big meeting will not armour-plate your immune system; the pattern that matters is a consistent habit over weeks and months.

For most people, two to four moderate sessions a week is a realistic and sensible target that also fits what the wider evidence suggests for general health. Build up gradually, keep sessions to a comfortable length, and rehydrate afterwards. Our guide to how often you should use a sauna goes into this in more detail, and what the evidence says about sauna health benefits covers the broader research.