A 30-minute sauna session may put an athlete’s immune system on higher alert. Finnish researchers found that sauna heat, paired with a short cold shower, increased every type of white blood cell circulating in the bloodstream, including key infection fighters such as neutrophils and lymphocytes.

A new Finnish study suggests that spending time in a sauna can temporarily move more white blood cells into the bloodstream. These immune cells help the body detect and respond to pathogens and disease.

Researchers found that a 30-minute sauna session increased the number of every type of circulating white blood cell. Participants briefly cooled down under a cold shower halfway through the session.

Levels of neutrophils and lymphocytes, two important parts of the immune system, returned to their usual levels within about 30 minutes after the sauna ended.

"This may indicate that sauna bathing mobilizes additional white blood cells into the bloodstream from tissues, where they are then redeposited after the session. This kind of periodic release of white blood cells into the bloodstream is beneficial, as once they leave their storage sites, they are better able to patrol the body and respond to pathogens," says Ilkka Heinonen, an Academy Research Fellow at the University of Turku.

A similar release of white blood cells happens during physical exercise. By sending more of these cells into circulation, the body may improve immune surveillance and strengthen its ability to respond to possible threats.

More Research Needed

Regular sauna use has been linked to a range of health benefits in other research studies. The temporary immune changes observed in this study could help researchers understand some of the biological processes behind those associations.

The researchers caution that the experiment measured only the immediate effects of a single sauna session. The findings cannot establish whether repeated sauna bathing produces lasting changes in immune function or long-term health.

The study included 51 adults with an average age of 50. The findings were published in Temperature, a scientific journal focused on the medical physiology of body temperature regulation.