Hot water immersion more than doubles core body temperature rise compared to traditional saunas, potentially boosting vasodilation, cardiac output, and immune activity. Digest
Passive heat therapies, such as hot baths and saunas, raise core body temperature and activate physiological responses that support cardiovascular and immune health, including increased cardiac output, enhanced vasodilation, and elevated immune activity, which may help reduce inflammation. A recent study found that hot water immersion raised core temperature by approximately 1.1°C (2°F)—roughly twice the increase seen with a traditional sauna and considerably more than with a far-infrared sauna.
The study included 20 healthy adults, half of them women, who each completed three sessions of passive heating spaced at least one week apart. The sessions included 45 minutes in hot water at 40.5°C (105°F), three 10-minute rounds in a traditional sauna at 80°C (176°F), and 45 minutes in a far-infrared sauna, ranging from 45°C to 65°C (113°F to 149°F). Researchers measured core temperature every five minutes, assessed heart function before, midway, and after each session, and collected blood samples to examine inflammatory markers and immune cells up to 48 hours after each session.
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Hot water immersion caused the greatest physiological changes, including the largest rise in core body temperature—about 1.1°C (2°F)—compared to just 0.4°C (0.7°F) with the traditional sauna and essentially no change with the far-infrared sauna. Cardiac output increased by 3.7 liters per minute with hot water immersion, roughly 60% more than that observed with the traditional sauna. It was also the only method to provoke a detectable immune response, including a post-heating rise in interleukin-6 levels and an increase in the numbers of natural killer cells and CD8+ T cells 24 to 48 hours later. The other two modalities induced smaller or negligible changes in these measures.
This small study’s findings suggest that hot water immersion is the most effective method for raising core temperature and stimulating cardiovascular and immune responses. Soaking in a hot bath also improves deep sleep. Learn more in this episode featuring Dr. Rhonda Patrick.