In his latest book, 'The Doctor', Dr Karl Kruszelnicki explains how hot tea can help cool you down.
It takes energy – heat – to make sweat, and it takes lots more energy to make it evaporate.
I first heard (and wrongly disagreed with) the cooling effect of tea while studying Physics. I thought adding extra heat from the steaming cuppa would simply make things hotter.
I didn’t understand sweat. Back then, I had no idea of how the body worked – it would be at least 10 years before I learnt any Physiology.
When you drink hot tea, it can trigger temperature sensors in your mouth that activate sweating. (These are TRPV1 receptors. They also get activated by chilli, as in curry.) Tiny droplets of sweat exude from your skin all over your body – which takes energy. The surrounding hot air evaporates the sweat – and, thanks to the Laws of Physics, this takes lots of energy. The droplets of sweat sit on your skin, so your skin cools as they evaporate.
But evaporation won’t work on a very humid day. When there’s a lot of water vapour already in the air, the water in the sweat on your skin won’t evaporate easily. It will probably just soak into your clothes, or drip to the ground.
Of course, the effectiveness of a hot cuppa also depends on how hot your drink is, how much you drink, the temperature of the day, if you’re exercising, and more.
So on a hot and humid day, if you’re exercising hard and generating more sweat than evaporation can remove, you’re probably better off with a cold drink.
But, under the right circumstances, a nice cuppa can cool you down. And so might a hot curry.
About the author: Dr Karl Kruszelnicki is the Julius Sumner Miller Fellow at the University of Sydney. He is a qualified medical doctor, engineer, physicist and mathematician. He consistently appears on the list of the Top 15 Most Trusted Australians, and has been named one of Australia's National Living Treasures.
Click here for more information about Dr Karl's latest book, 'The Doctor'.