Who doesn’t love a long, hot shower at the end of a tiring day? Or – perhaps more relevant right now – an icy cold one in the middle of a heat wave? Well, as with everything humans enjoy, science has looked into our showering proclivities to see what exactly is going on.
It turns out hot and cold showers have very different effects on the body – and there is a better way to do it.
For most of us, a hot shower is the go-to bathing option. And according to an analysis presented at the 2018 Joint International Conference on Water Distribution System Analysis and Computing and Control for the Water Industry, most of us have fairly predictable preferences when it comes to shower temps – we like the water to be between 40 and 41°C (104 and 106°F), on average.
That points to one obvious benefit of showering at the top end of the thermometer – it’s just nicer. They’re relaxing: studies have shown that hot showers can help us sleep better, and hot water can also help relieve body tension, muscle fatigue, and maybe even long-term conditions like osteoarthritis.
Hot showers can also improve circulation. When exposed to heat, the body’s blood vessels widen, and immersion in warm water has been shown to improve arterial stiffness – a major factor in the development of cardiovascular conditions – and improve blood flow in people with chronic heart failure.
But hot showers aren’t without drawbacks: “Hot water strips the skin of its natural oils leading to dry, itchy skin and eventually eczema,” dermatologist Sejal Shah told Women’s Health. “Similarly, hot water can strip the hair of its natural oils, causing it to be drier.”
And that effect of lowering blood pressure can be a double-edged sword. “I must have heard a similar story at least a dozen times; a person is taking a hot shower, feels lightheaded and wakes up in a pool of blood from a head injury,” wrote interventional cardiologist Hassan Makki for CIC Centers.
It’s called vasovagal syncope, Makki explained, and hot showers are a prime place for it to happen.
“The heat has already caused a lot of the blood to be shifted to the superficial tissues (a mechanism the body uses to cool down)” Makki wrote. “With less blood available in tank so to speak, even a slight dip in blood pressure can cause syncope.”
So what about cold showers? They’re reputedly good for calming untoward urges – in fact, doctors in the 18th and 19th centuries would prescribe them, quite violently sometimes, as a cure-all for whatever they deemed “insanity.”
But is there any hard scientific data supporting their healthfulness? In fact, there is – although not in the treatment of mental illnesses. There are several studies that have pointed to an immune-boosting effect of cold showers, although the mechanism behind it is not completely understood yet – it may have something to do with the sympathetic nervous system, which is triggered by cold water and activates our fight-or-flight reflex.
“When this is activated, such as during a cold shower, you get an increase in the hormone noradrenaline,” explained Lindsay Bottoms, a Reader in Exercise and Health Physiology at the University of Hertfordshire, in an article for The Conversation. “This is what most likely causes the increase in heart rate and blood pressure observed when people are immersed in cold water, and is linked to the suggested health improvements.”
Cold water showers can also improve circulation – though not, as hot showers do, as a direct effect of the water itself. Instead, it’s thought to happen after the cold water stops: the body has to work extra hard to warm itself back up again, prompting more blood flow to the skin.
And when there’s extra effort being expended, there’s extra calorie loss. Really cold water – water at temperatures as low as 14°C (57°F) – has been shown to increase metabolism by a factor of 4.5, prompting claims that cold showers can boost weight loss. Adding to that effect is the idea that brown fat – the type of fat thought to hold the key to beating obesity – is both activated by cold temperatures and stored mostly around the shoulders and neck, making it seemingly perfect for a showery weight-loss treatment.
And finally, there’s the mental benefits of a cold shower. “There is a school of thought that cold water immersion causes increased mental alertness,” Bottoms wrote, noting that cold water applied to the face and neck has been shown to improve brain function in older adults.
“A cold shower may also help relieve symptoms of depression,” she added. “A proposed mechanism is that, due to the high density of cold receptors in the skin, a cold shower sends an overwhelming amount of electrical impulses from peripheral nerve endings to the brain, which may have an anti-depressive effect.”
But again, there are dangers to super-cold bathing. “Submerging in freezing cold water could cause the body to go into cold-water shock,” Glen Coulson, a health and water expert from Cladding Direct, told Metro.
“[That] could cause a number of reactions – from hyperventilation to heart attacks.”
Which is better – a hot shower, or a cold one?
If both ends of the temperature scale have benefits, what’s the optimum choice? Health experts are pretty united on this question, it seems – and the answer is an anticlimactic “somewhere in the middle”.
“The best solution is to take a warm, tepid shower and then finish off with cold rinse for the last few seconds to still reap the rewards of the cold water,” dermatologist Carl Thornfeldt told The Healthy.
And if, in the latest heat wave, you’re showering to cool off, make sure you don’t go too crazy. “[Cold water] won’t actually lower the body’s core temperature – which is what the body is working desperately hard to stabilize during the heatwave,” Coulson said.
“It’s always recommended to have a lukewarm shower, rather than indulging in a cold one.”
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