A recent study published in the journal Temperature reports that a single 30-minute Finnish sauna session can quickly mobilize immune cells, with changes observed within minutes of heat exposure, according to findings released on Apr. 17.
The research offers new insights into how controlled heat stress from sauna bathing may affect the human immune system. Understanding these effects could help clarify why regular sauna use has been linked to various health benefits.
The study involved 51 middle-aged adults who regularly used saunas and had at least one cardiovascular risk factor but no known cardiovascular disease. Participants were exposed to dry air at temperatures between 70 and 100 degrees Celsius for half an hour. The researchers found that circulating white blood cell counts increased rapidly during the session, while most cytokine levels remained unchanged immediately after exposure.
"FSB involves exposing people to relatively dry air at 70–100 °C for 10-30 minutes per session. It is part of Finnish culture and is shown to offer multiple health benefits," the authors said in their report. Among women, hemoglobin and hematocrit levels were lower than men’s before the session but increased afterward in both sexes. Platelet counts also rose post-sauna, with white blood cell increases particularly notable among female participants.
The researchers observed that neutrophil and lymphocyte counts returned to baseline within thirty minutes after leaving the sauna, while a combined group of other white cells (monocytes, eosinophils, basophils) remained slightly elevated. Only two cytokines decreased significantly post-session; another showed a borderline increase. Body temperature measured at the ear was correlated with some cytokine changes but not with overall white cell count.
The authors noted limitations such as not measuring all subtypes of immune cells separately or assessing long-term effects beyond acute responses seen shortly after sauna use. They suggested further research should investigate whether these short-term physiological responses contribute to longer-term health outcomes and explore differences between habitual users and those less accustomed to heat stress.
