A latest Finnish study shows that a short period of sauna bathing will not only increase the heart rate and body temperature, but also significantly increase the number of circulating white blood cells in the blood in the short term, which may temporarily strengthen the body's "first line of defense" immune monitoring capabilities. The study, led by the University of Eastern Finland, included 51 adult participants with an average age of approximately 50 years.
In the study design, participants took a 30-minute Finnish sauna session, followed by a short cold shower break. The results showed that after the sauna ended, all types of circulating white blood cells in the blood of the subjects increased, including neutrophils and lymphocytes, which are regarded as the core defense force. However, the numbers of these two key cell types fell back to baseline levels within about 30 minutes, indicating that the effect was short-lived.
The research team pointed out that sauna does not "newly generate" more immune cells in a short period of time, but more like mobilizing white blood cells originally stored in tissues and temporarily dispatching them into the blood circulation. "This may mean that sauna bathing mobilizes extra white blood cells from the tissues into the blood and then returns to the original storage site again after it is over." said Ilkka Heinonen, a researcher at the Academy of Sciences of the University of Turku in Finland. He believes that this periodic "mobilization of troops" will help immune cells patrol more extensively in the body and more effectively monitor and respond to potential pathogen threats.
The researchers pointed out that this phenomenon of large amounts of white blood cells entering the blood in a short period of time is quite similar to what is observed in the human body during physical exercise. During strenuous activities, the body will also increase the number of circulating immune cells to enhance the effectiveness of "immune patrol." This finding further strengthens the idea that some lifestyle interventions that have cardiovascular and metabolic benefits may also improve immune function through similar pathways.
In addition to white blood cell counts, the research team also measured the levels of various cytokines in the participants' blood. Cytokines are key signaling molecules involved in immune responses, but overall, a single sauna bath did not trigger significant overall changes in blood cytokine levels. However, the research team found that the extent to which an individual's body temperature rose during the sauna period was correlated with changes in the levels of several cytokines, but this correlation was not observed between the number of white blood cells and changes in body temperature. "Interestingly, some of the changes in cytokines seem to be related to the increase in body temperature during the sauna process," said Jari Laukkanen, professor at the University of Eastern Finland and leader of the study.
Multiple epidemiological and clinical studies in the past have suggested that regular sauna use may be associated with many health benefits, including improved cardiovascular health and reduced risk of death. This study attempts to explain some of the biological mechanisms that this traditional lifestyle may bring about from an immunological perspective. However, the research team also emphasized that this trial only examined the "acute effects" of a single sauna bath, and therefore could not make conclusive conclusions about long-term health outcomes.
A related paper has been published in the academic journal "Temperature" published on March 31, 2026, titled "Acute Finnish sauna heat exposure induces stronger immune cell responses than cytokines" (tentative translation). The study pointed out that larger-scale clinical studies with long-term follow-up are still needed in the future to clarify whether sauna habits of different frequencies and different intensities can be transformed into tangible public health benefits through immune regulation pathways.