Their answer, in short: Yes, a hot drink can cool you down, but only in specific circumstances. “If you drink a hot drink, it does result in a lower amount of heat stored inside your body, provided the additional sweat that’s produced when you drink the hot drink can evaporate,” Jay says.
How does this work? “What we found is that when you ingest a hot drink, you actually have a disproportionate increase in the amount that you sweat,” Jay says. “Yes, the hot drink is hotter than your body temperature, so you are adding heat to the body, but the amount that you increase your sweating by—if that can all evaporate—more than compensates for the the added heat to the body from the fluid.”
The increased rate of perspiration is the key. Although sweat may seem like a nuisance, the body perspires for a very good reason. When sweat evaporates from the skin, energy is absorbed into the air as part of the reaction, thereby cooling the body. A larger amount of sweat means more cooling, which more than counteracts the small amount of heat contained in a hot beverage relative to the entire body.”