A Finnish study reports that a single 30-minute sauna session, with a brief cold shower midway, temporarily increases circulating white blood cells. The rise includes neutrophils and lymphocytes that are central to immune defense. Counts return to baseline within half an hour. The pattern is consistent with enhanced immune surveillance during and immediately after heat exposure, according to Medical Dialogues.
The study, led by Professor Jari Laukkanen at the University of Eastern Finland, involved 51 adults. There were 27 women and 24 men, with an average age of 50. Participants underwent multiple blood draws after spending 30 minutes in a Finnish sauna at 73 degrees Celsius, with a brief cooling period under a cold shower halfway through.
Immediate rise in circulating white blood cells
The immediate rise in all circulating white blood cells during the session, followed by a return to baseline shortly afterward, was consistent across participants. The findings align with evidence that the body can mobilize additional white blood cells from tissues into the bloodstream during stressors such as heat exposure and physical exercise. This can enhance immune surveillance and bolster frontline defense against pathogens. Circulating white blood cells are a key component of the body’s protection against a range of diseases. Their short-term release into the bloodstream allows them to patrol more effectively and respond quickly to potential threats.
Researcher Ilkka Heinonen noted that this periodic mobilization is beneficial because, once they leave their storage sites, these cells are better positioned to detect and counter pathogens as they circulate. The study’s timeline—an acute rise during the 30-minute session with a mid-session cold exposure, followed by normalization within half an hour—suggests a transient immune-activation window rather than a sustained elevation.
Observational data associated regular sauna bathing with lower rates of fatal cardiovascular events. A Canadian-Finnish observational study has also indicated a potential link between regular sauna use and improvements in respiratory, cognitive, and cardiovascular health. Clinicians have pointed to possible mechanisms tied to heat exposure, including greater relaxation, lowered blood pressure, and better vasodilation, which is the widening of blood vessels, according to the New York Post.
In Finland, sauna bathing is widely ingrained in daily life as a space for cleansing, rest, and retreat. Many in northern Europe practice contrast therapy that pairs extreme heat with extreme cold as part of everyday routines believed to support sustained mental, physical, and emotional wellbeing. The ubiquity of the tradition is reflected in the country’s scale of infrastructure: an estimated 3.3 million saunas serve a population of 5.5 million.