October 11, 2026, 3:55 pm | Read time: 6 minutes
Those prone to low blood pressure likely enter the bathtub with great caution, if at all. It’s well-known that a hot bath can significantly affect circulation: It causes blood vessels to dilate, temporarily lowering blood pressure further. But could this effect be beneficial for people with generally high blood pressure? A new study specifically examined how a 30-minute hot bath impacts blood pressure and circulation compared to 30 minutes of moderate exercise. The latter is often not feasible for older individuals with severe obesity (and often high blood pressure).
Regular exercise is crucial for health, not just in combating obesity. Physical activity improves the function and elasticity of blood vessels, as well as their ability to respond to changes. It’s believed that heat is behind this effect—specifically, the rise in body temperature from exercise. The heat-induced dilation of skin vessels increases blood flow through the skin, raising the mechanical stress on the vessel walls—a process known as shear stress.
Study examines heat from exercise vs. passive heat
People with physical limitations can hardly achieve these effects through exercise. This study therefore explored the potential of passive heat treatment.1 Previous research has shown that repeated heat treatments can improve certain vascular functions.2
The researchers posed the question: Does the effect of a 30-minute hot bath on skin microcirculation match that of an equally long moderate cycling session? And does this apply similarly to men and postmenopausal women?
Details of the study
This was a relatively small study, with 25 participants (10 men, 15 women) aged 45 to 70. All participants were at least overweight or already obese, and none were regularly physically active. Only postmenopausal women were allowed to participate to account for possible hormonal influences. Exclusion criteria included various underlying conditions (such as cardiovascular diseases and type 2 diabetes) and physical limitations that made participants unsuitable for the cycling part of the study.
The study was designed as a randomized crossover study. Each participant had to undergo both conditions: a “warm water immersion”—in this case, a stay in a warm bathtub—and moderate exercise on a stationary bike. At least 72 hours had to pass between the two parts of the study. The order in which participants bathed or exercised was randomly determined, allowing for comparison of the results of the two interventions within the same person.
30 minutes of bathing vs. 30 minutes of exercising
Each intervention lasted 30 minutes. During the warm water part, participants were to lie in the hot bath with almost their entire body submerged. The water was to reach up to the sternum, and the arms had to be fully covered. The water temperature was 40 degrees Celsius. For the cycling part, the exercise was to be performed at an intensity of 60 to 70 percent of maximum heart rate.
How did the applications affect the vessels? To measure this, the researchers used an imaging technique called optical coherence tomography, or OCT. This allowed them to identify the small skin vessels and determine their diameter and density, as well as blood speed and flow. Measurements were taken before and immediately after each intervention on the participants’ forearms. Additionally, the researchers recorded core body temperature, heart rate, and blood pressure during the interventions.
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Bathing surprisingly effective
The authors found significantly greater changes in all OCT measurement parameters after the hot bath compared to cycling. On average, the diameter of the skin vessels increased by 5.2 ± 4.3 micrometers after the 30-minute bath—compared to only 1.1 ± 3.7 micrometers after cycling.
Changes in blood flow velocity were also more pronounced after the hot bath: It increased by 22.8 ± 11.7 micrometers per second. After cycling, it even slightly decreased by 1.2 ± 4.5 micrometers per second. Blood flow showed a similar pattern. After the hot bath, it increased by 68.9 ± 29.8 picoliters per second, while after exercise, it decreased by 8.3 ± 13.8 picoliters per second.
Finally, the difference in the change in the density of perfused skin vessels after the two applications was statistically significant. After the hot bath, it increased by 14.1 ± 7.8 percent. In response to cycling, it decreased by 3.1 ± 4.8 percent.
Regarding core body temperature, it rose similarly in both cases. After the hot bath, the increase was 0.9 ± 0.3 °C, and after exercise, it was 0.7 ± 0.3 °C. However, cycling increased heart rate more. The opposite effect occurred with blood pressure: It decreased more after the hot bath than after exercise.
The researchers confirmed their OCT measurements with another method, called laser Doppler flowmetry. This also showed that warm water promoted skin blood flow more than exercise.
Only immediate effects studied
The study results suggest that a 30-minute hot bath can significantly increase the blood flow in the smallest skin vessels in older people with overweight or obesity. This can have beneficial effects on blood pressure, among other things.
The warm water intervention and cycling exercise lasted the same amount of time but exerted different stimuli on the body. In the hot bath, the skin was directly warmed, and core body temperature also rose. The researchers conclude that both the direct warming of the skin and the overall higher heat load affected blood flow.
These observations could be particularly relevant for people with physical limitations. A warm water treatment could be an alternative to moderate exercise or a useful addition to physical activity within their capabilities.
However, the results should not be interpreted to mean that hot baths can completely replace exercise. The study only examined the body’s immediate reactions. Based on the observations, it is not yet possible to make statements about long-term benefits or lasting effects.
Limitations
Despite the striking values, the study’s significance is limited. This is mainly due to the small sample size. With 25 participants, it was small from the outset, and ultimately, OCT data from only 22 people could be evaluated because the images from three participants were of insufficient quality due to image errors. Reliable statements about differences between men and women cannot be made based on this sample. It is even less possible to generalize the observations to other population groups (such as younger people and those with normal weight).
It is also not clear which part of the effect is due to the heat and which to the respective intervention. The hot bath and cycling did not produce equally strong heat or circulatory stress. After the bath, both core body temperature and skin blood flow increased more than during exercise. Since the forearms were directly in the water during the bath, the skin areas used for measurement were also automatically warmed.
It remains unclear how long the observed changes lasted, as measurements were only taken immediately after the interventions. It would be premature to make any statements about whether regular hot baths have long-term health benefits.