According to a Science Daily article published on July 27, visiting a sauna triggers a temporary release of leukocytes into the bloodstream, helping the body detect and neutralize pathogens more actively.
The study involved 51 volunteers with an average age of 50. The experiment showed that a 30‑minute sauna session leads to an increase in the concentration of all types of leukocytes circulating in the blood. In the middle of the session, participants took a short break to take a cold shower. Meanwhile, the levels of neutrophils and lymphocytes — key cells for immunity — returned to baseline values about 30 minutes after the session ended.
Ilkka Heinonen (Finnish Academy of Science, University of Turku) suggests that sauna use promotes leukocyte mobilization: cells move from tissue “reserves” into the bloodstream, patrol the body more actively, and respond to threats, then redistribute back into tissues. This mechanism is somewhat similar to what happens during physical exercise: increased circulation of immune cells improves monitoring for potential pathogens and enhances the body’s readiness to respond.
Researchers also monitored the dynamics of cytokines — molecules that regulate immune activity. On average, the changes were insignificant, but individual responses depended on how much the participant’s body temperature rose. As study leader Jari Laukkanen (University of Eastern Finland) noted, the levels of several cytokines correlated with the rise in body temperature, while no direct link was found between temperature and leukocyte count.
At the same time, the authors emphasize that only the short‑term effect of a single sauna session was assessed in the study. Currently, there is insufficient evidence to claim that regular sauna use can lead to sustained changes in immunity or long‑term health improvements.
Risks should also be considered: on July 10, Olga Ulankina, an expert doctor at the Hemotest laboratory, warned in an interview with Izvestia about the dangers of visiting a bathhouse in hot weather. In high ambient temperatures, the load on thermoregulatory mechanisms increases sharply, and the additional heat in the sauna further complicates these systems’ work. People with cardiovascular conditions, uncontrolled hypertension, heart rhythm disorders, and severe lung diseases should be especially cautious.
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