A single sauna session may trigger a surprising response in the immune system. Researchers in Finland have discovered that spending just 30 minutes in a sauna, with a brief cold shower halfway through, causes white blood cells to surge into the bloodstream. These cells are essential to the body’s defenses, helping identify and fight infections and other potential threats.
The findings suggest that sauna bathing may temporarily mobilize immune cells that normally remain in tissues, allowing them to circulate more widely throughout the body. This increased movement could help the immune system monitor for harmful pathogens, including bacteria and viruses.
During the study, researchers observed an increase in every type of circulating white blood cell they measured. Among them were neutrophils and lymphocytes, two important groups of immune cells. Neutrophils are often among the first defenders to respond to an infection, while lymphocytes include cells that recognize specific threats, produce antibodies, and help coordinate immune responses.
The increase was temporary. Within 30 minutes after the sauna session, neutrophil and lymphocyte counts had returned to their original levels.
How Sauna Bathing May Activate Immune Defenses
“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 process is known as immune surveillance. Rather than remaining in one location, immune cells travel through the bloodstream and tissues, searching for signs of infection or other abnormalities. By temporarily increasing the number of white blood cells in circulation, the body may improve their ability to detect potential threats.
Interestingly, a similar response occurs during physical exercise. Exercise can temporarily increase the number of immune cells moving through the bloodstream, helping distribute them throughout the body. The new findings suggest that sauna bathing may produce a comparable short-term response, although this does not mean the two activities provide identical immune benefits.
Sauna Heat Also Affects Immune Signaling Molecules
The researchers also investigated whether sauna bathing influenced cytokines, small proteins that help immune cells communicate with one another. Cytokines play important roles in regulating inflammation, coordinating immune defenses, and directing the body’s response to infections.
Overall, the sauna session produced little change in average cytokine levels in the bloodstream. However, a closer examination revealed an interesting connection between certain cytokines and changes in body temperature.
“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.
In other words, some immune signaling molecules responded differently depending on how much a person’s body temperature increased. White blood cell counts, however, did not show the same relationship with rising body temperature.
This distinction suggests that sauna bathing may influence different parts of the immune system through different physiological processes.
What This Discovery Means for Sauna Health Benefits
Previous research has linked regular sauna bathing with several potential health benefits. The latest findings offer another clue about what may be happening inside the body during these sessions, particularly how heat exposure and the sauna routine affect immune cell circulation.
However, the researchers caution that the results do not establish whether sauna bathing produces lasting improvements in immune function or reduces the risk of illness. The study examined only the immediate effects of one sauna session, and the observed changes in white blood cells were short-lived.
Because the session also included a brief cold shower, the findings reflect the combined sauna and cooling routine rather than the isolated effects of heat alone.
The research involved 51 adults with an average age of 50. The findings were published in the scientific journal Temperature, which specializes in research on body temperature regulation and its effects on human physiology.
Although more research is needed to understand the long-term implications, the study reveals that even a single sauna session can rapidly change how immune cells circulate through the body, potentially offering new insight into the biological effects of this popular relaxation practice.
