Researchers in Finland report that 30 minutes in a sauna, with a brief cold shower, briefly increased circulating immune cells in 51 adults, though lasting health effects remain unproven.
Researchers in Finland report that a single 30-minute sauna session, with a brief cold shower halfway through, caused white blood cells to surge into the bloodstream. The study, published in the journal Temperature, involved 51 adults with an average age of 50 and was led by Professor Jari Laukkanen of the University of Eastern Finland, with Ilkka Heinonen of the University of Turku among the researchers quoted. According to the university's summary of the work, every type of circulating white blood cell the team measured increased, including neutrophils, which are often early responders to infection, and lymphocytes, which help recognise specific threats and coordinate immune responses.
The rise was short-lived: within 30 minutes after the session, neutrophil and lymphocyte counts had returned to their starting levels. Heinonen suggested this may indicate that sauna bathing mobilises extra white blood cells from tissues into the blood, where they can patrol the body more effectively before being redeposited, a process known as immune surveillance. The response resembles the temporary rise in circulating immune cells seen during exercise, although the researchers stress this does not mean the two activities offer identical immune benefits. Average levels of cytokines, the signalling proteins immune cells use to communicate, changed little, but several cytokines varied with how much body temperature rose; white blood cell counts showed no such link.
The authors caution that the findings do not show whether sauna bathing improves immune function over the long term or lowers the risk of illness, because only the immediate effects of one session were examined. The protocol also included a cold shower, so the results reflect the combined sauna and cooling routine rather than heat alone. The details reported here come from the research team's published materials as relayed by ScienceDaily, and no independent replication was available at the time of writing. Further studies would be needed to understand whether regular sauna use produces lasting changes in how the immune system functions.
