“These benefits are particularly important as high blood pressure and poor artery function are among the leading causes of strokes and heart attacks,” says Dr Tom Cullen, an assistant professor at Coventry University’s Centre for Physical Activity, Sport and Exercise Sciences. His research has shown that these effects are comparable with exercise.

However, this doesn’t mean you ought to cancel your gym membership in favour of relaxing in the bath.

“Most research suggests that hot baths should complement, not replace, other healthy lifestyle habits such as regular exercise and a balanced diet,” says Steward, who also worked on this study.

“Exercise remains the most effective way to improve overall health, as it provides benefits that heat exposure alone cannot, including building muscle mass through repeated muscle contractions, reducing fat mass through increases in energy expenditure and strengthening bones through weight-bearing activity.”

However, a bath can still play a role in improving your heart health.

“I do believe that some additional heating via hot baths or saunas can be a nice additional healthy activity to improve certain aspects of health, particularly cardiovascular health,” Cullen says.

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Steward recommends taking a 39-degree bath for 30 minutes to an hour about three times a week for eight weeks, which should trigger improvements in blood vessel function and a drop in blood pressure.

“If you are happy to stay in for longer than that, then the benefits are likely to be better, but just be careful getting out of the bath as some people can feel a bit lightheaded,” Cullen says.

A hot bath can also contribute to dehydration, which can cause headaches and tiredness, so it’s worth having a glass of water nearby, the experts say.

“It needs to be more than just a bit lukewarm,” Leicht adds. “You should start to sweat a bit and, after 10 or 15 minutes, you should feel like you want to put a limb out of the water. That could be a helpful indicator if you don’t have a thermometer.”

To improve sleep: Take a 15- to 20-minute bath 90 minutes before bed

As well as helping you mentally wind down before bed, baths trigger physical effects that can make it easier to nod off and have a better quality of sleep.

“After you get out of a warm bath, there will be a difference between your skin temperature and your core temperature,” Leicht says. Our skin cools down quickly after being exposed to the air, while our core will remain warmer for longer, he says.

Research has linked this difference between core and skin temperature with better sleep, including falling asleep more quickly and an increase in rapid eye movement (REM) sleep, which is vital for brain function.

“The theory is that the cooling down after a hot bath helps to stimulate melatonin production in the hypothalamus [the part of the brain that regulates sleep cycles],” Cullen says. “Melatonin is the hormone that naturally makes us feel sleepy. It does this because melatonin is typically produced in the evening when our body temperature decreases.”

Studies suggest that taking a 15- to 20-minute bath about 90 minutes before going to bed will trigger these improvements in sleep, says Cullen.

“Another thing,” notes Leicht, “is that a bath just relaxes you, as your blood pressure comes down during a bath and your cortisol may drop as well.”

To reduce stress levels: Take a 15-minute bath when you need a mood boost

The benefits of a warm bath aren’t just physical – they can also improve your mood, research suggests. “In our studies, we have seen reductions in the stress hormone cortisol after a hot bath, which I think is likely to be what is causing the improvement in mood,” Cullen says.

There is also some evidence to suggest that a bath helps the body release feel-good chemicals such as endorphins and dopamine, Steward notes. It can also relax your muscles, leaving you feeling less stressed, he says.

“Some of the effects may be from being in the relaxed environment of a bath,” Leicht says, but studies also show that inflammatory markers (interleukin-6) can come down while submerged in water, which may also play a role in lifting mood.

To feel these effects, the bath can be shorter and cooler than that required for improved heart health, Cullen says. He recommends a 15-minute bath and a temperature of 38 to 39 degrees as often as you like. “I think it would be completely fine to judge for yourself when you have had enough,” he says.

The Telegraph, London

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