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In a study of 51 adults, a 30-minute sauna session with a brief cold shower halfway through was followed by increases in every measured type of circulating white blood cell. Neutrophil and lymphocyte counts returned to their starting levels within 30 minutes; the study did not test whether the routine prevents illness or improves immunity over time.
A study of 51 adults found that a single 30-minute sauna session, including a brief cold shower halfway through, was followed by a temporary rise in every type of circulating white blood cell the researchers measured. Neutrophil and lymphocyte counts returned to their original levels within 30 minutes after the session, and the findings do not show that sauna bathing prevents illness or produces lasting immune benefits.
The Finnish research team measured participants’ white blood cell counts before and after the sauna routine. The measured cells included neutrophils, which can respond early to infection, and lymphocytes, a broad group involved in recognizing threats, producing antibodies and coordinating immune responses. The report says the counts rose after the session, but the increase was short-lived.
Researchers also examined cytokines, proteins that help regulate communication among immune cells. Average cytokine levels showed little overall change. However, levels of several cytokines varied in relation to how much participants’ body temperatures rose. White blood cell counts did not show the same relationship with temperature change, according to the study report.
The authors interpret the rise in circulating cells as possibly reflecting movement of white blood cells from tissues into the bloodstream, followed by their return to tissues. That explanation is a proposed mechanism, not a demonstrated health outcome. The study measured an immediate biological response; it did not assess infection rates, disease prevention or long-term immune function.
A Short-Lived Shift in Immune Cells
The findings offer a measured look at how the body responds to one sauna-and-cooling routine. White blood cells circulate through blood and tissues as part of immune surveillance, so a temporary change in their numbers in the bloodstream may help researchers study how heat exposure affects their movement. It does not, by itself, establish that the body is better protected from infection.
The result also helps distinguish a laboratory measure from a claim about health. A higher count in a blood sample is not proof of stronger immunity, and the reported return to starting levels within 30 minutes underscores the brief time window observed. The research may inform further study of sauna physiology, but it offers no basis for replacing established medical advice or treating sauna bathing as an infection-prevention method.
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The Sauna Routine and Study Group
The study involved 51 adults with an average age of 50. Participants completed a 30-minute sauna session with a brief cold shower halfway through. The research therefore concerns the combined routine: the findings cannot isolate the effects of sauna heat from those of cooling.
The results were published in Temperature, a journal focused on body-temperature regulation and its effects on human physiology, according to the source report. Previous research has associated regular sauna bathing with potential health benefits, but this experiment focused on immediate changes after one session, not outcomes from regular use.
The researchers compared the immune-cell response with changes that can occur during exercise, when immune cells may temporarily increase in the bloodstream. That resemblance does not establish that sauna bathing and exercise have identical effects or provide equivalent health benefits.
“This may indicate that sauna bathing mobilizes additional white blood cells into the bloodstream from tissues, where they are then redeposited after the session.”
— Ilkka Heinonen, Academy Research Fellow at the University of Turku
Long-Term Effects Remain Untested
The study does not establish whether the temporary rise in circulating white blood cells leads to lasting changes in immune function, fewer infections or any other clinical benefit. It also does not show whether repeated sauna sessions produce the same response over time.
Because participants took a cold shower during the session, the results cannot identify how much of the observed response came from heat, cooling or their combination. The supplied report does not provide details such as the precise size of each cell-count change or enough information to determine how broadly the findings apply beyond this group. The proposed movement of cells from tissues into blood remains an interpretation of the observed pattern.
Further Research Must Test Outcomes
The next research step is to test whether the short-term blood-count changes are repeatable and whether they have any lasting significance. Studies comparing sauna exposure alone with routines that include cooling could help separate the effects of each part of the session. Research following participants over longer periods would be needed to assess responses to regular use.
Until such evidence is available, the finding should be read as a report of an immediate, temporary change in measured immune cells—not proof that sauna bathing prevents illness. The source report does not specify a planned follow-up study or publication date for additional results.
Key Questions
What did the sauna study find?
After a 30-minute sauna session with a brief cold shower halfway through, researchers observed an increase in every type of circulating white blood cell they measured in 51 adults. Neutrophil and lymphocyte counts returned to their original levels within 30 minutes.
Does this prove sauna bathing prevents infections?
No. The study measured short-term blood-cell changes. It did not test whether participants got fewer infections or whether their immune function improved over time.
Did the researchers test sauna heat by itself?
No. Participants took a brief cold shower halfway through the session, so the findings reflect the combined routine and cannot isolate the effect of heat alone.
How long did the white blood cell increase last?
The report says neutrophil and lymphocyte counts had returned to their starting levels within 30 minutes after the session. It does not establish how the response would differ after repeated sessions.
What did the study find about cytokines?
Average cytokine levels changed little overall, but levels of several cytokines were associated with how much body temperature rose. The researchers reported no similar temperature relationship for white blood cell counts.
Source: sciencedaily.com
