A single sauna session sends immune cells surging through your body
A new Finnish study reveals that just 30 minutes in a sauna can temporarily flood the bloodstream with additional white blood cells, potentially helping the immune system patrol the body and detect threats. The surprising response resembles the immune boost seen during exercise and may help explain some of the health benefits linked to sauna bathing.
Key points
- A 30-minute sauna session with a brief cold shower halfway through caused white blood cell counts to rise in 51 adults with an average age of 50.
- The increase was temporary, with neutrophil and lymphocyte counts returning to original levels within 30 minutes after the session.
- Researchers say the study does not show lasting immune improvements or reduced illness risk, and the routine included cooling as well as heat.
Researchers in Finland found that a single 30-minute sauna session, with a brief cold shower halfway through, caused white blood cells to surge into the bloodstream. Every type of circulating white blood cell measured increased, including neutrophils and lymphocytes, which help identify and fight infections.
The rise was short-lived: neutrophil and lymphocyte counts returned to their original levels within 30 minutes after the session. The study involved 51 adults with an average age of 50 and was published in the journal Temperature.
How researchers explained the effect
Ilkka Heinonen, an Academy Research Fellow at the University of Turku, said the results suggest sauna bathing moves white blood cells from tissues into the blood, where they are "redeposited" afterward. He said this periodic release is beneficial because the cells can better patrol the body and respond to pathogens once they leave their storage sites.
The article describes this patrol as immune surveillance. A similar temporary response occurs during physical exercise, which also increases immune cells in the bloodstream, though the article says this does not mean the two activities give identical immune benefits.
This kind of periodic release of white blood cells into the bloodstream is beneficial
— Ilkka Heinonen
Cytokines and body temperature
The session produced little change in average cytokine levels, but several cytokines changed in relation to how much body temperature rose. White blood cell counts showed no such association with temperature change, according to the article.
Professor Jari Laukkanen, who led the study at the University of Eastern Finland, said the findings suggest sauna bathing may affect different parts of the immune system through different processes. The researchers cautioned that the work examined only the immediate effects of one session and did not establish lasting benefits or a lower risk of illness.
