It is often said that drinking hot drinks (especially hot tea) on a hot day will cool you down. However, this claim is challenged almost as much as it is asserted. After all, it seems illogical that drinking something hot would make you feel cool, right? But it seems that there's hard science behind the old wives' tale after all.

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 (if you aren't wearing too much clothing or wearing clothing that doesn't allow perspiration to evaporate).

Why? Drinking hot drinks makes you sweat disproportionately more, which means that your body is putting out a LOT more sweat that 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 of your body. That means that for a hot drink to cool you down on a hot day, it needs to be a dry heat and you need to be wearing clothes that will allow the sweat to evaporate (or no clothes, for that matter!).

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. On 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, which is why chili peppers, hot sauce and the like can send some into a sweating frenzy (and why the same claim of a cooling effect on a hot day is made about spicy foods).

To summarize, when you drink a hot drink on a hot day, a sensor in your tongue and throat perceives the heat and causes the body to overreact with lots of sweat. If the sweat can evaporate, you cool down. If not, you don't.