A brief sauna session may quietly mobilize the immune system.
A sauna session may do more than raise your heart rate and body temperature. A new study from Finland found that it also briefly increases the number of white blood cells moving through the bloodstream, a shift tied to the body’s frontline immune defenses. The study involved 51 adults with an average age of 50.
After a 30-minute sauna session that included a short cold shower break halfway through, researchers saw an increase in all circulating white blood cells. Two of the most important groups, neutrophils and lymphocytes, returned to baseline within about 30 minutes.
Temporary Mobilization of Immune Cells
Rather than creating new immune cells, the sauna appears to temporarily move existing ones into circulation. That matters because white blood cells are most useful when they are actively traveling through the body, where they can detect signs of infection or other threats.
“This may indicate that sauna bathing mobilizes additional white blood cells into the bloodstream from tissues, where they are then redeposited after the session. This kind of periodic release of white blood cells into the bloodstream is beneficial, as once they leave their storage sites, they are better able to patrol the body and respond to pathogens,” says Ilkka Heinonen, an Academy Research Fellow at the University of Turku.
This short-term increase in circulating immune cells is similar to what happens during physical activity. It reflects the body’s ability to improve immune surveillance by sending more white blood cells through the bloodstream, where they can detect and respond to potential threats.
Cytokines and Temperature Effects
The researchers also examined cytokines, which are signaling molecules involved in immune responses. Overall, sauna use did not significantly change cytokine levels in the blood.
“Interestingly, however, the levels of several cytokines changed in relation to how much body temperature rose during sauna bathing. No similar association was observed between white blood cell counts and changes in body temperature,” says Professor Jari Laukkanen, who led the study at the University of Eastern Finland.
Regular sauna use has been linked to various health benefits, and these findings may offer insight into the biological processes behind those effects. However, the researchers note that this study focused only on the immediate impact of a single sauna session. Because of this limitation, the results do not establish any long-term health outcomes.
Reference: “Acute Finnish sauna heat exposure induces stronger immune cell than cytokine responses” by Ilkka H.A. Heinonen, Tiia Koivula, Maija Hollmén, Jaakko Immonen, Setor K. Kunutsor, Sirpa Jalkanen and Jari A. Laukkanen, 31 March 2026, Temperature.
DOI: 10.1080/23328940.2026.2645467
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