One sauna session, a surge of white blood cells

What happens to your immune system in the sauna? A team at the University of Eastern Finland set out to measure it directly.

The study

The research was published in Temperature in 2026. Participants took a single 30-minute dry sauna, with a brief cold shower midway through.

The team tracked white blood cell counts and cytokine levels in the blood across the session and the recovery that followed.

What they found

Circulating white blood cells rose during the session. That included neutrophils and lymphocytes, two of the body's key infection-fighting cell types.

Within about 30 minutes after the session, counts had returned to baseline.

Cytokines, the signalling molecules of the immune system, changed very little on average, though the changes tracked with how much body temperature rose.

How to read it

The researchers interpret this as mobilisation. Immune cells appear to move from tissues into the bloodstream during heat, then move back.

Exercise produces a similar pattern. The body treats the stress as a moment to put its defences into circulation.

This is interesting biology. It helps explain some of the mechanisms that might sit behind the long-term associations seen in Finnish sauna research.

What it does not say

It does not say that sauna prevents illness. It does not say one session "boosts immunity" in a lasting way. The change was short-lived, and the study was designed to observe it, not to follow people over months.

We think that distinction matters. The honest version of this finding is still a good reason to enjoy the ritual.

The cold interval

The protocol included a short cold shower in the middle. That rhythm of heat, brief cool, heat again is how most Finns bathe.

At home, that can be a shower, or a short dip in an N-02 set to a mild temperature. Keep the cold short, and do not bathe if you are already unwell with a fever.

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Sources

1. Medical Xpress, Sauna heat sends white blood cells surging through your bloodstream, study finds (2026)
2. ScienceDaily, A single sauna session sends immune cells surging (University of Eastern Finland)

This article is general information, not medical advice. If you have a heart condition, low blood pressure or are pregnant, speak with your GP before using heat or cold.