Study Finds One Sauna Session Triggers Rapid Increase in Infection-Fighting White Blood Cells

A single 30-minute sauna session may temporarily increase the number of immune cells circulating in the bloodstream, according to a new study. Researchers found that sauna bathing, combined with a brief cold shower, triggered a rapid rise in white blood cells, suggesting a possible connection between heat exposure and immune system activity.

Published in the journal Temperature, the study conducted by researchers in Finland investigated how sauna bathing influences immune cell circulation and inflammatory signalling molecules.

The study involved 51 adults with an average age of 50 years. Participants underwent a 30-minute sauna session that included a brief cold shower halfway through.

Researchers measured changes in circulating white blood cells, including neutrophils and lymphocytes, which play important roles in protecting the body against infections.

The findings revealed that all measured types of white blood cells increased temporarily following sauna bathing.

Neutrophils, which help the body respond to infections, and lymphocytes, which recognise harmful pathogens and coordinate immune responses, showed noticeable increases in circulation.

However, these changes were short-lived. Within 30 minutes after the sauna session, neutrophil and lymphocyte levels returned to their original values.

Researchers suggested that sauna bathing may temporarily mobilise immune cells from body tissues into the bloodstream, allowing them to circulate more widely and potentially support immune surveillance.

The team also examined cytokines, proteins involved in immune communication and inflammation.

Although average cytokine levels showed little overall change, certain cytokines varied according to the increase in body temperature during sauna bathing.

Interestingly, white blood cell changes were not similarly associated with temperature increases, suggesting different underlying physiological mechanisms.

However, the study assessed only the immediate effects of one sauna session and did not determine whether sauna bathing improves long-term immunity or prevents infections.

REFERENCE: Ilkka H.A. Heinonen, Tiia Koivula, Maija Hollmén, Jaakko Immonen, Setor K. Kunutsor, Sirpa Jalkanen, Jari A. Laukkanen. Acute Finnish sauna heat exposure induces stronger immune cell than cytokine responses. Temperature, 2026; 13 (2): 186 DOI: 10.1080/23328940.2026.2645467