A sauna session may do more than leave you feeling relaxed and warm. New research from Finland suggests that spending just 30 minutes in a sauna can trigger a noticeable response in the immune system, sending additional white blood cells into the bloodstream.
Researchers at the University of Eastern Finland found that a single sauna session, followed by a brief cold shower halfway through, temporarily increased the number of circulating immune cells. These cells help the body recognize and respond to infections, making their movement through the bloodstream an important part of the body’s natural defenses.
Published in the scientific journal Temperature on October 28, 2026, the study offers a closer look at how heat exposure affects the immune system. However, the changes did not last indefinitely, and researchers have not established whether regular sauna bathing leads to lasting improvements in immunity.
A Single Sauna Session Changed the Number of Immune Cells in the Blood
The researchers wanted to understand how sauna bathing affects the body’s immune response. They examined 51 adults with an average age of 50, measuring different types of white blood cells before and after a sauna session.
The participants underwent a 30 minute sauna session that included a brief cold shower halfway through. The researchers then examined changes in the number of immune cells circulating in their blood.
The results showed an increase in every type of circulating white blood cell measured during the study. Two particularly important groups were neutrophils and lymphocytes, which perform different jobs in protecting the body against potential threats.
Neutrophils are among the immune system’s first responders during an infection. They help defend the body against invading microorganisms, while lymphocytes are specialized cells that recognize specific threats, produce antibodies, and coordinate immune responses.
However, the increase was temporary. Within 30 minutes after the sauna session, neutrophil and lymphocyte counts had returned to their original levels.
Why Having More White Blood Cells in Circulation Matters
An interesting part of the discovery is that the additional white blood cells may have come from tissues where they were already present.
According to Ilkka Heinonen, an Academy Research Fellow at the University of Turku, sauna bathing may temporarily mobilize immune cells from their storage locations into the bloodstream. After circulating through the body, these cells can return to tissues.
This movement is important because immune cells do not simply remain in one location waiting for an infection. They travel through the bloodstream and different tissues, looking for signs of harmful microorganisms and other abnormalities.
Scientists call this process immune surveillance. It allows the body’s defenses to monitor different areas and respond when potential threats are detected.
The temporary increase in circulating white blood cells could therefore help distribute immune cells more widely throughout the body. However, the study did not establish whether this movement actually improves a person’s ability to fight an infection.
Related: 10 Powerful Immune-Boosting Foods for a Stronger Immune System
Sauna Bathing May Produce an Immune Response Similar to Exercise
The researchers also noted an interesting similarity between the effects of sauna bathing and physical exercise.
Exercise is already known to temporarily increase the number of immune cells circulating in the bloodstream. As the body becomes more physically active, immune cells move into circulation, changing how they are distributed throughout the body.
The new findings suggest that sauna bathing may trigger a comparable response.
This does not mean sitting in a sauna provides the same benefits as exercising. The two activities affect the body differently, and the researchers have not established that they produce identical immune responses.
Nevertheless, the similarity offers another way to understand how the body responds to different physical conditions. Both activities can influence immune cell movement, even though one involves physical exertion and the other involves heat exposure.
Researchers Also Examined How Heat Affects Immune Signaling
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White blood cells were not the only part of the immune system investigated during the study. The researchers also measured cytokines, small proteins that allow immune cells to communicate and coordinate their activities.
Cytokines help regulate inflammation and direct different parts of the immune response. Their levels can tell researchers how the body responds to various physiological changes.
Interestingly, the sauna session produced little change in average bloodstream cytokine levels. However, the researchers noticed that several cytokine levels were related to how much participants’ body temperatures increased during the session.
Professor Jari Laukkanen, who led the study at the University of Eastern Finland, explained that this relationship was not observed with white blood cell counts.
In other words, some immune signaling molecules appeared to respond according to the extent of the increase in body temperature, while the number of circulating white blood cells did not show the same pattern.
This suggests that different components of the immune system may respond to sauna exposure through separate physiological processes.
Does This Mean Regular Sauna Use Can Strengthen Immunity?
The findings offer another possible explanation for the biological effects associated with sauna bathing. However, they do not establish that spending time in a sauna prevents infections or provides lasting protection against illness.
One important distinction is that the researchers examined the immediate response to a single session. The increase in circulating immune cells was temporary, with neutrophil and lymphocyte counts returning to their original levels within 30 minutes.
The study also involved a cooling period with a cold shower. This means the observed changes reflect the combined sauna and cooling routine, not heat exposure alone.
Researchers would need to conduct further investigations to determine whether repeated sauna sessions produce different effects or lead to lasting changes in immune function.
For now, the study provides evidence that even one sauna session can influence how immune cells circulate through the body. It also highlights the immune system’s complexity, which responds to changes in temperature and physical activity in ways scientists are still working to understand.
