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Just 30 minutes in a sauna can temporarily flood your bloodstream with white blood cells, a new Finnish study finds. The immune surge — which mirrors what happens during exercise — may help the body better patrol for infections. Counts returned to baseline within 30 minutes of stepping out.
Think of your next sauna session as a mini workout for your immune system. Researchers at the University of Eastern Finland found that a single 30-minute sauna session (with a brief cold shower midway) caused every type of measured white blood cell — including neutrophils and lymphocytes — to surge into the bloodstream. The effect is thought to reflect a temporary mobilization of immune cells from tissues into circulation, where they can more effectively scan the body for pathogens like bacteria and viruses.
The response closely resembles what happens during physical exercise, when heat and physiological stress similarly push immune cells into the bloodstream. Interestingly, while white blood cell counts spiked uniformly, certain cytokines (immune signaling proteins) responded differently based on how much each person's body temperature rose — suggesting sauna heat may engage multiple immune pathways through distinct mechanisms.
By the Numbers
Why it matters: This research offers a biological explanation for some of sauna's long-touted health benefits, though researchers caution that short-term immune changes don't yet confirm lasting protection against illness. More studies are needed to determine long-term immune implications.
