A single sauna session of just 30 minutes can produce rapid changes in the immune system, according to a study by Finnish researchers.
Scientists have discovered that exposure to heat, interrupted by a cold shower, causes a temporary increase in the number of white blood cells, cells essential to the body’s defense against infection. The effect resembles one of the immune responses seen during exercise.
The research, carried out by specialists from the University of Eastern Finland and the University of Turku, provides new clues about how the sauna influences the body.
The results were published in the scientific journal Temperature and presented on October 28, 2026 by ScienceDaily.
Although previous studies have linked regular sauna use to certain health benefits, the biological mechanisms involved are not yet fully understood.
The new research suggests that one of these could be the rapid mobilization of immune cells from tissues into the bloodstream.
What researchers discovered after just one sauna session
The study included 51 adults, 27 women and 24 men, with an average age of about 50 years.
Participants spent 30 minutes in a Finnish sauna at a temperature of 73 degrees Celsius. Halfway through the session they took a short break for a cold shower.
The scientists collected blood samples before the exposure, immediately after it ended and 30 minutes after exiting the sauna.
The analyzes followed the changes in the number of white blood cells and some substances involved in the communication between the cells of the immune system.
The results showed a significant increase in the total leukocyte count immediately after the session.
Increases were also observed in the case of neutrophils and lymphocytes, two categories of cells with an essential role in protecting the body.
Neutrophils participate in rapid defense against pathogens, while lymphocytes are involved in, among other things, threat recognition, antibody production, and coordination of immune responses.
The effect wore off in just 30 minutes
One of the most interesting results was the short duration of the observed changes.
Approximately 30 minutes after exiting the sauna, the neutrophil and lymphocyte counts had returned to baseline values.
Other categories of white blood cells, such as monocytes, eosinophils, and basophils, remained elevated for a slightly longer period.
The researchers believe that these changes do not necessarily indicate the production of more immune cells.
One possible explanation is that the sauna causes the mobilization of white blood cells from the tissues and from the areas where they are stored, allowing them to circulate temporarily in greater numbers through the blood.
Later, they are redistributed in the body.
Ilkka Heinonen, a researcher at the University of Turku, explained that this periodic mobilization could improve the immune cells’ ability to monitor the body and identify potential threats.
The process is known in medicine as immune surveillance and involves the circulation of specialized cells through the blood and tissues to identify pathogens or other abnormalities.
The sauna produces a similar response to exercise
The researchers noticed that the identified phenomenon resembles a process that occurs during physical activity.
Exercise can temporarily mobilize immune cells, increasing their number in the bloodstream.
Thus, the body can redistribute its defense cells to more effectively police different tissues.
The results suggest that exposure to sauna heat in combination with the cool-down break may elicit a comparable physiological response in some respects.
However, experts point out that this does not mean that the sauna can replace physical exercise or that it offers the same benefits on the immune system.
The study only looked at biological changes immediately after a session, not long-term health effects.
Body temperature rose from 36.4 to 38.4 degrees Celsius
The researchers also monitored changes in body temperature during the session.
On average, it rose from 36.4 to 38.4 degrees Celsius as a result of exposure to heat.
The specialists tried to determine whether the extent of the temperature increase influences the response of the immune system.
To this end, they also analyzed 37 cytokines, substances that transmit signals between immune cells and participate in the regulation of inflammation and defense reactions.
The results showed that only two of the analyzed cytokines significantly changed their concentrations after the session.
However, the researchers identified 18 statistical associations between changes in body temperature and levels of certain cytokines.
In contrast, the increase in white blood cell count did not show the same relationship with body temperature.
This difference suggests that the mobilization of immune cells and the alteration of chemical signals involved in immunity could be influenced by distinct physiological mechanisms.
Can the sauna strengthen the immune system?
The results provide a possible explanation for some of the benefits previously associated with regular sauna use.
Observational research has identified links between sauna use and certain favorable outcomes for cardiovascular health and mortality.
However, the new study does not prove that the sauna reduces the risk of infection, prevents disease or improves the body’s ability to fight pathogens.
A temporary increase in the number of white blood cells does not automatically mean that the immune system is getting stronger.
The researchers only looked at the immediate response to a single session and did not assess whether people who regularly went to the sauna got sick less often.
Furthermore, the experiment included both heat exposure and a cold shower, so the effects of the two interventions cannot be separated with certainty.
The authors believe that further research is needed to determine whether repeated immune cell mobilization produces long-term clinical benefits.
Who should be cautious with the sauna
Although the sauna is well tolerated by many healthy adults, exposure to high temperatures can cause dehydration, low blood pressure, dizziness, or other unwanted reactions.
People with unstable cardiovascular conditions, uncontrolled blood pressure or other important medical problems should consult their doctor before using the sauna.
Hydration is also important, and exposure should be discontinued if dizziness, weakness, or malaise occurs.
The 30-minute duration used in the study represents the experimental protocol and should not be interpreted as a general recommendation.
