A Hot Bath Outperformed Exercise in a New Study on Blood Vessels (But You Should Still Exercise)

Hot water dramatically increased blood flow through the skin's tiniest vessels.

Thirty minutes on an exercise bike sounds like a better cardiovascular workout than thirty minutes sitting in a hot bath. But when scientists looked at what was happening inside the tiny blood vessels beneath people’s skin, they found something surprising. The bath produced a far greater increase in blood flow than cycling.

In a new study, researchers at the University of Western Australia found that immersing the body in hot water caused small blood vessels to widen and dramatically increased circulation through the skin.

The findings, published in the European Journal of Applied Physiology, add to growing evidence that passive heating can stimulate the cardiovascular system in ways that resemble some effects of exercise. They also raise an intriguing question: Could something as simple as a hot bath help keep our blood vessels healthy?

What happens to your blood vessels in a hot bath?

The researchers recruited 25 adults, averaging 59 years old, who were overweight or had diagnosed obesity and exercised relatively little. Each participant completed two experiments on separate days.

In one session, they pedaled a stationary bicycle for 30 minutes at moderate intensity. In the other, they spent the same amount of time immersed up to their chest in water heated to 40°C (104°F), with their arms submerged.

Before and immediately after each session, the team examined the tiny blood vessels beneath the skin of the forearm. They used optical coherence tomography, a noninvasive imaging technique that uses light to reveal structures too small to see with the naked eye.

The results were striking.

After the hot bath, the tiny blood vessels beneath the skin widened, blood moved through them faster, and more of the vascular network became active. Cycling, meanwhile, produced little change in blood flow through the forearm and actually reduced the proportion of small vessels carrying detectable blood.

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Perhaps the most revealing finding concerned perfused vessel density — essentially, how much of the scanned tissue contained tiny blood vessels with detectable blood flow.

After hot-water immersion, this measure increased by 14.1% on average. After cycling, it decreased by 3.1%.

This doesn’t mean a hot bath creates new blood vessels in half an hour. Rather, heating appears to open up more of the existing microvascular network to detectable blood flow.

Why hot water sends blood rushing through your skin

Blood does much more than deliver oxygen and nutrients. It’s also essential in regulating body temperature.

When you get hot, blood vessels near the skin’s surface widen in a process called vasodilation. More warm blood reaches the skin, allowing your body to shed heat into the surrounding environment.

During a hot bath, however, the water itself is supplying heat. Your body responds by increasing circulation to the skin as it struggles to maintain a stable internal temperature.

Meanwhile, exercise does something different.

As muscles contract, they require additional oxygen and nutrients. The cardiovascular system must distribute blood to those working muscles while also helping control body temperature. Consequently, circulation in a relatively inactive region, such as the forearm during cycling, may behave differently from circulation in muscles doing the work.

There’s another important aspect. The researchers submerged the participants’ forearms and arms in the hot water, directly warming the very tissue they later examined. Cycling warmed the body internally but did not expose the forearms to the same local heating.

That helps explain why the bath produced such a dramatic response in the skin’s tiny vessels. It also means the findings shouldn’t be interpreted as proof that bathing provides a better cardiovascular workout.

As blood flows through vessels, it exerts a gentle frictional force on their inner walls, known as shear stress. This stimulates processes that help regulate blood-vessel function, including the production of nitric oxide, a molecule that encourages vessels to relax.

Repeated exposure to these forces may help blood vessels adapt over time. The question is whether regularly heating the body can produce lasting improvements.

Can regular hot baths actually improve cardiovascular health?

It’s not the first time researchers highlighted hot baths as a way to help your cardiovascular health.

In a separate 2026 trial, 31 relatively inactive adults underwent 12 weeks of regular hot baths, cycling, or no intervention. Both bathing and cycling improved a measure of blood-vessel function compared with baseline, although only exercise produced a statistically significant improvement over the inactive control group.

A 2025 study involving 24 adults also found that adding hot-water immersion after exercise improved certain blood-pressure and vascular-function measures more than exercise followed by cooler water.

Together, the findings suggest that hot baths may complement exercise, even if they can’t replicate all its benefits.

That possibility is particularly relevant for older adults and people with mobility limitations, who may find regular exercise difficult. Passive heating could offer a way to stimulate circulation without strenuous physical activity.

But exercise offers a wide array of benefits, and a hot bath can’t replace them all, especially when it comes to stronger muscles, improved endurance, and better metabolic health.

There are safety considerations too. Spending 30 minutes in 40°C (104°F) water can cause overheating, dizziness, or excessive drops in blood pressure, particularly in vulnerable individuals. The study’s protocol shouldn’t be treated as a general recommendation.

So, by all means, don’t stop exercising. Baths can’t replace that. But the research suggests that soaking in hot water may offer cardiovascular benefits of its own, particularly for people who struggle to stay physically active. And while you’re relaxing in the tub, your blood vessels may be getting quite a workout.

Journal Reference: Wigati, K. W., et al. (2026). Comparison between exercise and hot water immersion on skin microvascular responses in older adults with overweight and obesity. European Journal of Applied Physiology.