A single 30-minute sauna session, paired with a short cold shower, can increase every type of white blood cell circulating in the bloodstream, including key infection fighters such as neutrophils and lymphocytes, according to a study led by the University of Eastern Finland.
The researchers said their findings suggested that spending time in a sauna can temporarily move more white blood cells – which help the body detect and respond to pathogens and disease – into the bloodstream.
Participants had briefly cooled down under a cold shower halfway through the session, and levels of neutrophils and lymphocytes, two important parts of the immune system, returned to their usual levels within about 30 minutes after the sauna ended, the team noted.
“This may indicate that sauna bathing mobilises additional white blood cells into the bloodstream from tissues, where they are then re-deposited after the session. This kind of periodic release of white blood cells is beneficial, as once they leave their storage sites, they are better able to patrol the body and respond to pathogens,” said Ilkka Heinonen, an Academy Research Fellow at the University of Turku.
A similar release of white blood cells happens during physical exercise. By sending more of these cells into circulation, the body may improve immune surveillance and strengthen its ability to respond to possible threats.
Cytokine changes varied with temperature
The researchers also examined several cytokines, signalling molecules that help co-ordinate immune activity. Overall, the saunas produced only small changes in the average levels of cytokines circulating in the blood.
However, individual cytokine responses appeared to depend partly on how much a participant’s body temperature increased during the sauna session.
“Interestingly, however, the levels of several cytokines changed in relation to how much body temperature rose during the sauna. No similar association was observed between white blood cell counts and changes in body temperature,” said Professor Jari Laukkanen, who led the study at the University of Eastern Finland.
Longer term effects remain unclear
Regular sauna use has previously been linked to a range of health benefits, and the temporary immune changes observed in this study could help researchers understand some of the biological processes behind those associations.
Still, the researchers caution that the experiment measured only the immediate effects of a single sauna session. The findings cannot establish whether repeated sauna bathing produces lasting changes in immune function or long-term health.
The study included 51 adults with an average age of 50. The findings were published in Temperature, a scientific journal focused on the medical physiology of body temperature regulation.
Study details
Acute Finnish sauna heat exposure induces stronger immune cell than cytokine responses
Ilkka Heinonen, Tiia Koivula, Maija Hollmén et al.
Published in the journal Temperature on 31 March 2026
Abstract
Regular exposure to Finnish sauna bathing (FSB) has been associated with reduced morbidity and mortality. This study aimed to examine the acute effects of FSB on immune cell mobilisation, circulating cytokines, and their associations with changes in body temperature. A total of 51 adults − 27 women (mean age 50 ± 9 years, body mass index (BMI) 27 ± 5 kg/m2) and 24 men (mean age 50 ± 10 years, BMI 27 ± 3 kg/m2) – were exposed to a 30-minute session of acute FSB at a temperature of + 73°C. Venous blood samples were collected at baseline, immediately after and 30 minutes after the FSB and analysed for immune cells and 37 cytokines. Subjects were allowed to drink water throughout. FSB increased body temperature from 36.4 ± 0.5°C to 38.4 ± 0.7°C, without altering plasma volume. Total white blood cell (WBC) count rose significantly and remained slightly elevated 30 minutes’ post-sauna in women. Neutrophil and lymphocyte counts increased immediately after the FSB but returned to baseline after 30 minutes, whereas MXD cells (monocytes, eosinophils, basophils) remained elevated. The levels of only two cytokines changed significantly. Although only a few correlations were observed between changes in immune cells and cytokines, 18 significant associations were identified between changes in body temperature and circulating cytokines – particularly immediately post-sauna – but not with WBC changes. Thus, a 30-minute session of acute FSB induces immune cell mobilization. The observed associations between changes in body temperature and circulating cytokines suggest that sauna-induced heat stress, along with immune activation, may partly mediate the health benefits of FSB.
See more from MedicalBrief archives:
Frequent saunas reduce the risk of stroke
Sauna benefits akin to those of medium-intensity exercise