Avoid cold shower on a hot day

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 not be helping the body cool off at all. Our body's optimal temperature is around 37°C. This temperature 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 per cent of our body heat is lost this way. Sweating is another mechanism the body uses.

Around 22 per cent 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.

Cold shower? Of course, when the weather gets 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 might be risky for some people. When exposed to cold, the blood vessels near to the skin constrict – reducing the blood flow into these areas.

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. 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 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.

On a hot day, a tepid or lukewarm bath or shower is the way to go; evidence suggests 26-27°C is most effective. 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 and 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.

(The writer is associated with Lancaster University)