30 minutes in a sauna temporarily raised white blood cell levels — ScienceAlert

In Finland, researchers recorded that after one 30-minute session in a traditional sauna, the number of white blood cells in participants' blood temporarily increased. The small experiment involved 51 middle-aged people. The results were published in the journal Temperature, ScienceAlert reports.

How the experiment was conducted

Participants spent 30 minutes in a Finnish sauna at a temperature of about 73 degrees Celsius. In the middle of the session, they took a cold shower. Immediately after the procedure, blood tests showed an increase in several types of white blood cells compared with pre-session levels.

In particular, the number of neutrophils, which are among the first to respond to pathogens, and lymphocytes, which are involved in forming immune memory, increased. The combined measure of monocytes, eosinophils, and basophils also rose. Monocytes absorb pathogens and cellular debris, while eosinophils and basophils are associated with inflammatory responses.

At the same time, cytokine levels — protein mediators of the immune system — changed only slightly on average. Some of them increased along with a rise in participants' body temperature.

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The effect faded quickly

Thirty minutes after the end of the session, most of the detected changes had nearly disappeared. Most white blood cell indicators returned to their previous level, although some changes in monocytes persisted. The researchers did not monitor participants for longer, so they cannot determine the duration of the effect or its impact on disease risk.

University of Turku researcher Ilkka Heinonen suggested that a sauna may mobilize additional white blood cells from tissues into the bloodstream, after which they return to sites where they accumulate. At the same time, the study did not analyze individual cell subtypes, including T cells and natural killer cells, which limits conclusions about the sauna's effect on immune function.

The body's responses to intense heat remain insufficiently studied. Previous observational studies linked regular sauna use to a lower risk of certain diseases, including pneumonia, but the current experiment does not prove a causal relationship.