One common factoid that has been circulating the internet recently is that drinking a hot beverage on a hot day will cool you down. Some immediately dismiss the claim while others swear by it.
The skeptical wonder how putting something hot into your body, while adding to its heat, could possibly cool it down. Proponents generally rely on anecdotal evidence that they have experienced first-hand. But who is right? Is there any actual scientific evidence behind this seemingly counter-intuitive claim?
Drinking something hot on a hot day can indeed cool you down, but there is a catch. A study done at the University of Ottawa’s School of Human Kinetics showed that if you were to drink a hot beverage in a hot and dry environment, your body will overcompensate for the added heat by sweating, and sweating a lot. It’s this excessive sweating that causes your body to cool down, and cooling it down more than if you had drunk something cold instead.
As long as you aren’t wearing layers of clothes, and your skin has room to breathe, the cooling effect of the evaporation of sweat is more than enough to cover the cost of the added heat to your body from the hot beverage. However, this cooling effect only works if the air is dry, rather than humid. You cannot sweat efficiently enough to take advantage of the benefit in a muggy or humid environment.
You may have already experienced this effect when eating hot or spicy foods. Research at the University of Cambridge studied the effects of certain foods and drinks on receptors on our tongue and in our throat. They discovered that one specific receptor, the TRPV1 receptor, was responsible for sensing heat and telling our body how to respond. In many individuals, the response is to produce excessive sweat.
This is the same reason why some people break out in a pouring sweat after eating extremely spicy chili or habanero peppers. If the air around you is dry and you’re wearing light clothes, eating foods spicy enough to cause a sweating reaction will also produce the same cooling effect as drinking a hot beverage.
So to recap, this myth isn’t a myth at all. Drinking something hot can in fact cool you down if the right conditions are met. Those conditions are: 1) It needs to be relatively hot outside; 2) The environment or air needs to be dry and not humid; 3) Your sweat must be able to evaporate off your skin normally without being restricted by clothing or other materials.
So there you have it. If you’re in humid Singapore, a hot cup of coffee isn’t going to do much to cool you off. However, if you’re in a dry Australian summer during one of their heat waves, it just might do the trick to cool you off against all logic.
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