Does Sauna Bathing Fight Off Colds? What the Research Actually Shows

You feel it after a good sauna session: warm, loose, weirdly clearheaded. It’s tempting to call that an immune boost and move on. The honest answer is more interesting than a marketing slogan, and it’s worth understanding before you start treating the sauna like a substitute for a flu shot.

What you need to know

Two separate bodies of research get mixed together in sauna folklore, and they answer different questions.

The first is an old but still frequently cited study from 1990, conducted in Austria and led by researcher E. Ernst. It followed 25 regular sauna bathers, one to two sessions a week, against 25 people who avoided sauna and similar heat exposure, over six months. The sauna group ended up with noticeably fewer colds overall, and the gap was largest in the final stretch of the study. Interesting detail: once someone in the sauna group did catch a cold, it didn’t last a shorter time or feel milder than in the control group. So the claimed effect, if real, looks like fewer infections taking hold, not a faster recovery once you’re sick.

That’s a small study from over three decades ago, and small trials like this are prone to noise. It’s suggestive, not proof.

The second line of research is newer and looks at what actually happens in your blood during and after a sauna session. A recent Finnish trial put roughly 50 adults, split fairly evenly between men and women in their late 40s and 50s, through a 30 minute sauna session at around 73°C (163°F). Researchers tracked white blood cells and inflammatory signaling molecules before, during, and after. Total white blood cell counts rose during the session, including neutrophils and lymphocytes, the cell types that patrol for and respond to pathogens. That rise wasn’t permanent: levels came back down within about 30 minutes of finishing.

The same research also found that certain immune signaling molecules changed in step with how much a person’s core body temperature rose, while the white blood cell increase itself didn’t track temperature the same way. In plain terms, your body seems to be running two related but somewhat separate immune responses to heat, and scientists are still working out how they connect.

What this does and doesn’t tell you

Here’s the honest gap: a temporary bump in circulating immune cells during a single sauna session is not the same thing as “sauna prevents colds.” Nobody has run a large, tightly controlled trial that isolates sauna use from all the other things that come bundled with a sauna habit, like regular exercise, better sleep, lower stress, and generally taking care of yourself. People who sauna two or three times a week are very often also the people doing a dozen other things that support their immune system. Untangling which part of that package does the work is genuinely hard, and the existing studies don’t fully manage it.

There’s also the practical fact that a 30 minute lab session in one controlled trial doesn’t map cleanly onto however you actually use your sauna. Ten minutes after work three times a week is a different exposure than a full traditional Finnish sauna evening with multiple rounds and cold plunges between them.

So treat the finding as this: regular sauna use is associated with fewer reported colds in at least one study, and a single session produces a measurable, short-lived shift in circulating immune cells. That’s a real physiological signal worth paying attention to. It is not evidence that sauna bathing prevents or treats infections, and it should never replace vaccination, seeing a doctor when you’re actually sick, or basic things like hand washing during cold and flu season.

How to actually use this

If you already sauna regularly, there’s no reason to stop on immune grounds, and the existing evidence gives you a reasonable feel good bonus to the habit. If you’re building a routine specifically hoping for fewer colds, here’s what a sensible approach looks like:

• Consistency over intensity. The cold study that found a benefit used regular, moderate sessions (one to two per week) over months, not occasional marathon sessions. A once a month blowout at 100°C is a different thing than a steady habit.
• Standard session length is fine. The immune cell response study used 30 minutes. You don’t need to push past your normal comfortable session length chasing some imaginary immune ceiling.
• Don’t sauna to “sweat out” an active infection. If you’re already running a fever, sauna heat adds cardiovascular and dehydration stress on top of what your body is already dealing with. Rest, fluids, and time do that job. Sauna when you’re healthy, as part of a routine, not as an emergency treatment once symptoms show up.
• Pair it with the basics. Sleep, hydration, and general activity levels almost certainly matter more for your immune system day to day than any single sauna session. Sauna is a nice addition to that foundation, not a replacement for it.
• Talk to a doctor if you have a real reason to. If you have a heart condition, are pregnant, or have any condition where heat stress is a concern, check with a doctor before making sauna a regular habit, immune benefits or not.

The takeaway

The research points to something real happening in your immune system during a sauna session, and one small older study found fewer colds among regular sauna users. That’s genuinely interesting and worth being curious about. It is not the same as proof that sauna bathing keeps you from getting sick, and anyone selling it to you as a guaranteed cold cure is overselling the science. Enjoy your sauna for what it reliably gives you: relaxation, better sleep, a nice ritual with friends or on your own. If it happens to shave off a cold here and there, consider that a bonus, not the reason you show up.