October 30, 2026, 1:14 pm | Read time: 6 minutes
Saunas can contribute to relaxation and are also considered beneficial for the immune system. But what mechanisms are behind this in detail? What changes occur immediately–after just one sauna session–and what role does the increase in body temperature play? In this context, Finnish researchers have gained intriguing insights in a study.
Saunas Affect the Immune System–But How?
One doesn’t do much more than sit in a sauna. However, this doesn’t mean it’s not strenuous. The body reacts to the heat with a significant cardiovascular load: The blood vessels in the skin dilate, the heartbeat accelerates, and more blood is pumped through the body. This is why saunas are not suitable for everyone with pre-existing health conditions.
For other conditions, such as depression, regular sauna visits could have a beneficial effect.1 Saunas are also associated with a lower risk of certain cardiovascular diseases, dementia, and respiratory diseases.2,3
A possible explanation for these connections is altered immune activity due to sauna use. Previous studies have already suggested that regular sauna use could reduce the concentration of the inflammatory marker C-reactive protein (CRP). Increases in white blood cells after sauna sessions have also been observed.4
The authors of the current study delved deeper into the specific processes.5 The aim of the investigation was to better understand how the body reacts immediately to the heat of the sauna.
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Details of the Study
Fifty-one adults from the Finnish city of Jyväskylä participated in the study. The average age of the 27 women was 50 ± 9 years, and the 24 men were on average 50 ± 10 years old. The average body mass index (BMI) in both groups was 27, which is classified as overweight.
The participants described themselves as symptom-free. Individuals with acute or pre-existing cardiovascular diseases were excluded, although the participating women and men had at least one objective risk factor for it (such as high blood pressure, elevated blood lipid levels, or a family history).
What Does a 30-Minute Sauna Session Do?
All participants had to sauna once for 30 minutes, with a two-minute shower scheduled halfway through. The average temperature of the sauna was 73 ± 2 degrees Celsius with a relative humidity of 10 to 20 percent. Participants were allowed to drink water both during the sauna session and in the subsequent 30-minute recovery phase.
The scientists took blood samples from the participants once before the sauna session, immediately afterward, and again 30 minutes after the sauna. Additionally, the body temperature was measured in the ear for both women and men.
Focus on White Blood Cells and Cytokines
In the blood, the researchers determined the number of different white blood cells and also the concentrations of 37 cytokines–these are important signaling molecules with which immune system cells communicate and coordinate their responses. Possible changes in blood plasma volume were also considered in the analysis. Blood plasma is the liquid component of blood–for example, fluid shifts can change its volume, which in turn can affect the concentrations of individual blood components.
Using statistical methods, the researchers examined changes over time and the relationships between temperature, immune cells, and cytokines. They also looked at differences between men and women.
Effect on Blood Cells
The measured ear temperature increased on average from 36.4 to 38.4 degrees Celsius. The researchers did not find a reduction in plasma volume.
However, what did happen: The total number of white blood cells increased significantly after the sauna session–in women, it was still slightly elevated 30 minutes later. Two important subgroups of white blood cells, neutrophils and lymphocytes, increased immediately after the sauna session but returned to their baseline values after 30 minutes. In contrast, a combined group of monocytes, eosinophils, and basophils remained elevated longer.
What Happens to Immune Signaling Molecules?
Among the 37 immune system signaling molecules studied, only two showed statistically significant changes: The levels of sCD30 and Pentraxin-3 decreased after the sauna session. A third signaling molecule (MMP-2) showed a trend toward an increase, but it narrowly missed the threshold for statistical significance.
The scientists found 18 significant correlations between the change in ear temperature and changes in cytokines. These were particularly strong immediately after the sauna. For 16 cytokines, a greater temperature increase was associated with higher values, while for two others, the relationship was reversed. No corresponding relationship was found between the change in temperature and the change in the number of white blood cells.
Overall, the scientists found no clear evidence that the immune responses studied fundamentally differ between women and men. Nor did the usual sauna habits of the participants seem to have a measurable impact on the responses studied. This means that the observed changes in immune cells and individual signaling molecules after the sauna session appeared regardless of how often the participants usually used the sauna.
Possible Significance of the Results
The study shows that the immune system’s responses to a sauna session cannot be explained by a single change. Different components react to the heat stress in varying degrees.
The scientists suspect that the heat stress and the associated immune responses could explain some of the often-described health benefits of sauna use. However, the study only describes what happens in the blood immediately after a sauna session and how the values develop during the subsequent recovery phase. It does not provide a basis for recommending a specific sauna frequency or duration to specifically strengthen the immune system.
Sauna users should be aware: A temporary increase in white blood cells does not automatically mean that the immune system becomes permanently stronger or more efficient. Nor can the results be interpreted to mean that a sauna session reduces inflammation or protects against infections. Rather, the study provides a possible approach to further explore the physiological mechanisms behind the health benefits of sauna use. And not least, whether the observed immune responses actually contribute to these benefits.
Limitations
With only 51 participants, the study group was relatively small, and the sample was also not very diverse: They were middle-aged adults from a single city in Finland with at least one cardiovascular risk factor. Therefore, the results are not readily transferable to all population groups.
Furthermore, only the effect of a single sauna session was studied. The study cannot make a statement about the effects of regular sauna use over months or years on the immune system or disease risk. Additionally, no control group without a sauna session was included.
It is also limiting to mention that the measurements were limited. The body temperature was determined in the ear–this does not measure the core body temperature. Additionally, the researchers combined several subgroups of white blood cells. Specific T-cell subgroups and natural killer cells, which play an important role in immune defense, were also not examined in detail.
Finally, only statistical correlations between temperature and cytokines were established. It cannot be concluded with certainty that the temperature change caused the observed signaling molecule reactions–nor that these reactions are beneficial to health.