It is often said that drinking hot tea or coffee on a hot day will cool you down. This claim is challenged almost as much as it is asserted. It does seem illogical that drinking something hot would make you feel cool. But there is actually hard science behind the old wives' tale after all. It may depend on where you live and how much you sweat and the actual weather conditions outside.
Thermodynamics, Biology, Hot Drinks, and Hot Weather
According to a research paper published by the University of Ottawa’s School of Human Kinetics, drinking hot drinks on hot, dry days can cool you down. The circumstances have to be ideal, but it is possible that a warm drink can reduce your body temperature.
Drinking hot drinks makes you sweat disproportionately more. This means that your body is putting out a lot more sweat than it should be given the rise in temperature involved. This overreaction can cool you down more than enough to offset the heat of the drink if the sweat can evaporate off your body. If the sweat cannot evaporate (because of the clothes you are wearing or due to the weather conditions near you), then the hot drink will not cool you down. It will probably just make you sweatier and hotter.
For it to work, these conditions need to exist simultaneously:
- The high temperatures are from dry heat. This trick will not work in muggy, humid weather.
- You need to be wearing clothes that will allow sweat to evaporate.
- While you could be naked (observing any public nudity laws, of course), your clothes should be as thin and light as possible.
The humidity is a key component here. You might have good luck with this method if you live in the hot, dry desert of Arizona or Utah, but if you're on the humid East Coast, it probably won't work.
It's All In the Tongue and Throat
Peter McNaughton, a neuroscientist at the University of Cambridge, built upon the understanding of why the body sweats so much more when you drink a hot drink on a hot day. It has to do with receptors on the tongue and in the throat. One particular receptor called the TRPV1 receptor senses heat and causes the body to respond with an overabundance of sweat. Interestingly, it also responds to spicy foods in the same way.
Putting It All Together
Let's put the science talk aside and expose this myth in plain English:
- When you drink a hot drink on a hot day, a sensor in your tongue and throat perceives the heat.
- This causes your body to overreact with lots of sweat.
- If the sweat can evaporate, you cool down. If not, you don't.
If a hot beverage on a hot day has no appeal, don't worry. Stick with refreshing cool beverages. You'll quench your thirst and stay hydrated.
Bain AR, Lesperance NC, Jay O. Body heat storage during physical activity is lower with hot fluid ingestion under conditions that permit full evaporation. Acta Physiol (Oxf). 2012;206(2):98-108. doi:10.1111/j.1748-1716.2012.02452.x
Yang F, Zheng J. Understand spiciness: mechanism of TRPV1 channel activation by capsaicin. Protein Cell. 2017;8(3):169-177. doi:10.1007/s13238-016-0353-7