A new scientific review suggests that hot water immersion, or passive heat therapy, may help lower blood pressure, but researchers caution that benefits are not consistent for everyone. Published in the Journal of Applied Physiology, the review analysed existing evidence on the effects of bathing in water heated to 39°C to 40°C, a practice used for centuries in Roman thermae, Japanese onsen and Turkish hammams.
The study found that longer sessions of hot water immersion were linked to greater reductions in blood pressure. However, typical bath water is between 33°C and 37°C, and temperatures above 40°C are not advised due to risk of overheating. To practice safely, researchers recommend leaving the bath gradually, having a seated recovery period, keeping limbs out of the water and staying well hydrated.
Older adults and people with treated hypertension experienced consistent benefits, while young, healthy individuals and those with untreated hypertension saw minimal or no sustained effects. The review also noted a 28% lower risk of cardiovascular disease in one observational study, but could not prove direct causation.
Beyond blood pressure, hot water immersion improved sleep quality, reduced stress markers and enhanced long-term psychological health. The researchers concluded that the therapy “shows promise” as a support for hypertension treatment, but should not replace medications. Further research is needed to define protocols, as long-term effects remain inconsistent.
