A third of adults live with a
high blood pressuresometimes despite medication and efforts on diet. In this context, the idea that a simple hot bath can help reduce blood pressure, especially when you feel too tired to exercise.
A vast review published in 2025 in the Journal of Applied Physiology has sifted through all the available data on thehot water immersion and tension. The authors consider the avenue promising, but point to small, heterogeneous and often imperfect studies. The hot bath does not work in the same way for everyone.
Hot bath and hypertension: what the studies really show
Most protocols define a hot bath as water at 39–40°C, compared to 33–37°C for so-called neutral water. During immersion, skin vessels dilate, blood flows to the periphery, vascular resistance drops and
blood pressure often decreases significantly.
A little reminder to correctly interpret the voltage figures
- Systolic pressure corresponds to the maximum pressure in the arteries when the heart contracts. If it is expressed as 11 for example, in reality but it is the abbreviated version of 110 millimeters of mercury (mmHg);
- Diastolic pressure is the minimum pressure when the heart relaxes between two contractions. As for systolic pressure, for example 8 corresponds to 80 mmHg.
The results of studies already conducted have given contrasting results:
- In older adults with osteoarthritis, 20 minutes in a bathtub at 40°C already lowered the average pressure by around 13 mmHg, with an extension of 10 minutes adding another 6 mmHg drop.
- Over several weeks, the image is more contrasted. A meta-analysis found on average only about 2 mmHg reduction in systolic pressure, but it is based on very few trials.
- Other studies describe reductions of 7 to 14 mmHg for systolic and 4 to 9 mmHg for diastolic after 4 to 12 weeks of repeated baths in elderly, sedentary or sick people (osteoarthritis, type 2 diabetes, arterial disease of the legs, heart failure).
- When blood pressure is measured continuously over 24 hours, the most reliable criterion, a trial in untreated hypertensive adults however showed no lasting drop.
Who benefits the most from a hot bath for their blood pressure?
In detail, the favorable effects mainly come back
in older people already being followed for hypertension or another cardiovascular disease. In a trial of seniors with osteoarthritis, those who took at least one antihypertensive medication saw their systolic drop by about 14 mmHg and their diastolic by 5 mmHg after 12 weeks of regular bathing, while participants without hypertension showed almost no change. Just five sessions of ankle immersion in water above 40°C were also enough to obtain a reduction of 14/9 mmHg in treated hypertensives.
In healthy young adults, responses are often modest. An 8-week program with five home baths per week in very warm water did not change resting blood pressure. Same mixed observation in adults with untreated hypertension, assessed by 24-hour ambulatory measurement. Some studies also find comparable reductions after immersion in only lukewarm water, which suggests that relaxation and water pressure also play a role. The answer therefore remains very individual.
How the hot bath acts on blood pressure… and how to use it safely
Heat dilates the arteries, increases blood flow to the skin and reduces the resistance the heart faces. This increased friction of blood against the wall stimulates the production of nitric oxide, which helps the vessels relax. With repeated sessions, factors like VEGF increase by around 60%, promoting the creation of new small vessels. Researchers also observe a shift towards a calmer nervous system, a moderate expansion of blood volume, less oxidative stress, better sleep and a reduction in certain stress markers.
The authors of the review insist:hot water immersion must remain a complement, never a substitute for medication or physical activity. They recommend baths around 39–40°C, approximately 30 minutesrather than waters at 42–43°C, which are associated with discomfort and, in Japan, thousands of drownings among elderly people in winter. Going out slowly, staying hydrated, avoiding alcohol and seeking medical advice in the event of a weak heart or severe hypertension remain essential reflexes.