Humans have long combatted the heat by eating spicy food. And while it may seem counterproductive to chow down on something searingly hot while baking in the sun, there’s sound evidence to suggest it will help you cool down.
The secret is sweat. Chilis like cayenne, jalapeño, ghost peppers, and habaneros get their heat from the chemical capsaicin. When you ingest capsaicin, it triggers a neural response from your body. Spicy foods excite (activate) the receptors in the skin that normally respond to heat. The central nervous system reacts to whatever the sensory nervous system tells it is going on. Therefore, the pattern of activity from pain and warm nerve fibers triggers both the sensations and the physical reactions of heat, including vasodilation, sweating, tearing up, and flushing.
You know the friend who can eat incredibly spicy food? They very likely enjoy hotter foods on a regular basis. Our reaction to hot peppers is governed by a neurotransmitter called substance P (P is for pain; my personal shorthand). In one of nature’s many tricky ways, substance P can be depleted slowly and takes time, many days, possibly weeks, to replenish, meaning that if you eat hot foods often, you literally build up a tolerance for hotter and hotter foods as your ability to consume them comfortably goes up.
The “burn” you feel in your mouth from eating spicy food can be followed by a similar warming sensation across the rest of your body, causing you to sweat as you eat. Sweating is one of the primary methods the human body has evolved to regulate temperature; specifically, it’s the evaporation of sweat that removes heat from your body. The longstanding idea of taking a hot shower before going to bed comes from the effect of heating and then cooling down your body temperature, which emulates REM sleep. It is relaxing. So as long as you stay hydrated while eating spicy food, the perspiration that comes from enjoying a delicious bowl of hot chili or curry forces your body to cool itself quickly and more efficiently. Interestingly, the burn from Capsaicin does not diminish by drinking water. Instead, consuming dairy, rice, and alcohol reduces the flames.
Eating very spicy food also triggers endorphins, our natural pain relievers. Eat spicy food regularly enough, and you start to associate the pain of hot peppers with the endorphins’ pleasant rush, akin to the runners’ “high.” Here’s to salsa, sriracha, and serranos. They literally make us feel better.
Also see The Psychology of Scotch Bonnets.