Written by Alison Proffitt
Researchers in Finland sought to determine the extent to which the practice of Finnish sauna bathing (FSB) reduces morbidity and mortality rates. They found that a sauna bath releases white blood cells into the bloodstream, which play a major role in the body’s defense against pathogens and various diseases. The study was published last week in the journal temperature (DOI: 10.1080/23328940.2026.2645467).
Heat stress poses a major physiological challenge to the human body; However, regular sauna bathing, as a form of controlled heat exposure, has been linked to health benefits. The study aims to explore potential mechanisms behind these benefits, the researchers wrote.
Researchers studied 51 adults (27 women, 24 men) with an average age of 50 years who were exposed to a 30-minute session of acute FSB at temperature 73°C with a short cooling shower halfway through. Venous blood samples were collected at baseline, immediately after 30 Minutes after FSB, immune cells and 37 cytokines were analyzed. Participants were allowed to drink water throughout.
The researchers found that a sauna session increased the number of circulating white blood cells. “My total white blood cell (WBC) count rose significantly and remained slightly elevated at 30 Minutes after the sauna for women. The number of neutrophils and lymphocytes increased immediately after FSB but returned to baseline after 30 minutes, while MXD cells (monocytes, eosinophils, and basophils) remained elevated.
Ilkka Heinonen, an academic research fellow at the University of Turku and first author of this paper, looked at the implications. “This may indicate that the sauna bath mobilizes additional white blood cells from tissues into the bloodstream, where they are redeposited after the session. This type of cyclic release of white blood cells into the bloodstream is beneficial, because once they leave their storage sites, they are better able to patrol the body and respond to pathogens,” she said in a statement.
In addition to immune cells, the researchers also measured levels of several cytokines, which act as mediators of immune defense. On average, sauna bathing had little effect on circulating cytokine levels.
“Interestingly, however, the levels of several cytokines changed in relation to how much body temperature rose during a sauna bath,” says Professor Jari Laukkanen, who led the study at the University of Eastern Finland. “No similar association was observed between white blood cell counts and changes in body temperature.”
The study, which is based on a single sauna session, has limitations. The authors hypothesize that regular sauna users may have different outcomes than those who used it rarely. Regular sauna users are more heat-adapted, but no specific conclusions can be drawn about the development of long-term health effects from a single session. But clearly, the authors wrote, a 30-minute hot bathing session in a Finnish sauna stimulates immune cell mobilization. “The association between changes in body temperature and circulating cytokine levels suggests that heat stress and immune activation may partially, but certainly not completely, mediate the beneficial health effects of sauna baths,” they assert.
