Just one sauna session can trigger a surprising response from the immune system. Finnish researchers found that by spending just 30 minutes in a sauna, with a brief cold shower halfway through, white blood cells enter the bloodstream. These cells are essential to the body’s defenses, helping to identify and fight infections and other potential threats.
The results 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 detect harmful pathogens, including bacteria and viruses.
During the study, researchers observed an increase in each type of circulating white blood cell 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. Less than 30 minutes after the sauna session, the neutrophil and lymphocyte counts had returned to their original levels.
How sauna baths can activate the immune system
“This may indicate that sauna bathing mobilizes additional white blood cells into the bloodstream from the tissues, where they are then redeposited after the session. This type of periodic 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,” explains Ilkka Heinonen, a researcher at the University of Turku Academy.
This process is known as immune surveillance. Rather than staying in one place, immune cells travel throughout the bloodstream and tissues, looking for signs of infection or other abnormalities. By temporarily increasing the number of circulating white blood cells, the body can improve its ability to detect potential threats.
Interestingly, a similar response occurs during physical exercise. Exercise can temporarily increase the number of immune cells circulating in the bloodstream, helping to distribute them throughout the body. The new findings suggest that sauna bathing may produce a comparable short-term response, although this does not mean that the two activities provide identical immune benefits.
Sauna heat also affects immune signaling molecules
The researchers also studied whether sauna bathing influenced cytokines, small proteins that help immune cells communicate with each other. Cytokines play an important role in regulating inflammation, coordinating immune defenses, and directing the body’s response to infections.
Overall, the sauna session produced little change in average blood cytokine levels. However, a closer look revealed an interesting link between certain cytokines and changes in body temperature.
“However, it is interesting to note that the levels of several cytokines changed depending on the increase in body temperature during sauna bathing. No similar association was observed between the number of white blood cells and changes in body temperature,” explains Professor Jari Laukkanen, who led the study at the University of Eastern Finland.
In other words, certain immune signaling molecules reacted differently depending on how much a person’s body temperature increased. However, white blood cell count did not show the same relationship with increasing 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 the benefits of sauna
Previous research has linked regular sauna bathing to several potential health benefits. The latest findings offer another clue to what may be happening inside the body during these sessions, particularly how heat exposure and the sauna routine affect the circulation of immune cells.
However, the researchers caution that the results cannot establish whether sauna therapy produces lasting improvements in immune function or reduces the risk of disease. The study only looked at the immediate effects of a sauna session and the changes seen in white blood cells were short-lived.
Since the session also included a brief cold shower, the results reflect the combination of the sauna and cool-down routine rather than the isolated effects of heat alone.
The research involved 51 adults with an average age of 50. The results were published in the scientific journal Temperature, which specializes in research into the regulation of body temperature 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 quickly change the way immune cells circulate in the body, potentially offering new insights into the biological effects of this popular relaxation practice.
Gn Health
