When the weather warms up, many of us use a nice cold shower to help us cool down. But while this might feel like relief, it might actually not be helping the body cool off at all.
Author
- Adam Taylor
Professor of Anatomy, Lancaster University
Our body's optimal temperature is around 37°C . This temperatures ensures our body systems can function properly. But when the core gets too hot the temperature regulating centre of the brain starts sending nervous signals out to the blood vessels and muscles in or near the skin - telling them to start activating their cooling mechanisms.
If our core stays at high temperature for too long (around 39-40°C), this can lead to organ damage . So to ensure our temperature stays optimal, the body uses multiple techniques to cool itself down.
For instance, the body radiates heat into the surrounding environment by electromagnetic (thermal) radiation. Approximately 60% of our body heat is lost this way.
Get your news from actual experts, straight to your inbox. Sign up to our daily newsletter to receive all The Conversation UK's latest coverage of news and research, from politics and business to the arts and sciences.
Sweating is another mechanism the body uses. Around 22% of our body heat is lost this way. But when the air temperature around us exceeds our body temperature, sweating becomes the dominant mechanism for reducing core temperature. Any remaining body heat is then lost through a mixture of convection into the air or liquid the body may be in contact with and conduction into solid objects that the body may be in contact with.
To support these mechanisms, our blood vessels change diameter . The ones closest to the skin dilate (widen) to allow more blood into them so they can get close to the relatively cooler surface of the skin.
The body then works to circulate the blood so that heat from inside the body can be moved to the periphery to cool off. Similarly on our skin, the hairs remain flat to allow air next to the body to cool and be replaced, helping to dissipate heat .
Cold shower?
Of course, when the weather gets really hot outside, these mechanisms just don't feel like they cut it.
Although diving into a cold bath or shower straight after being out in the heat might feel nice on your skin, it isn't doing what is needed to reduce the core temperature of the body. It might also be risky for some people.
When exposed to cold, the blood vessels near to the skin constrict - reducing the blood flow into these areas.
So in the context of cooling the body down, jumping into a cold shower does the opposite of what needs to happen, as less blood is now flowing to the surface of the skin. This will hold the heat in and around your organs instead of getting rid of it. Basically, you're tricking your body that it doesn't need to cool down, but actually needs to conserve heat.
And, depending on how cold your water is, sudden exposure could even trigger dangerous consequences for some people.
Exposure to water that is 15°C can trigger the cold shock response. This causes the blood vessels in the skin (those in contact with the cold water) to constrict rapidly. This increases blood pressure as the heart is now pumping against increased resistance.
This response can be particularly dangerous in people with underlying heart conditions , such as coronary artery disease. The cold shock response can also lead to an irregular heartbeat and even death when going from very hot to cold .
Thankfully, these events are rare - and probably won't happen if you're just taking a cold shower or bath in your home. But you might want to skip the cold plunge or avoid taking an ice bath on a hot day for this reason.
Hot showers are also a bad idea on a warm day. Although it's sometimes said that a hot shower helps the body cool down faster, this unfortunately isn't true. Water that is warmer than the body is going to transfer energy in the form of heat into the body . This again prevents the body getting rid of heat - potentially increasing its core temperature.
On a hot day, a tepid or lukewarm bath or shower is the way to go, evidence suggests 26-27°C is most effective. This helps bring blood to the surface to cool, without being cold enough to cause the body to think it needs to conserve its heat.
Another reason to skip a cold shower on a hot day is that it might not help you get clean.
When we get hot, we sweat - and this sweat mixes with sebum, another skin product and the bacteria on our skin, which produces body odour . Cold water has been shown to be less effective at removing and breaking down sebum and other detritus on the skin, compared to warmer water, which means body odour will persist.
Cold water also causes the skin to tighten. This might potentially trap sebum and dirt within the pores. This can lead to blackheads, whiteheads and acne. But warm or lukewarm water can help dissolve and loosen material in the pores.
As you plan your escape and recovery from the heat this week, a lukewarm or cool shower or bath, rather than a cold shower, is a safer and more effective choice. This will allow your body to dissipate heat away from your core without harm.
Equally, if you do feel the need to go cooler, do it gradually so you aren't shocking the body's automatic temperature regulation system into action. Turning the temperature down gradually if you want to go cold, or slowly placing a limb in at a time can help with this process.
Adam Taylor does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
