eli5: What does chili (and other spicy things) actually do to the tongue to make it feel hot?
In: Biology
We evolved sensors for heat because heat can cook flesh. Spicy stuff is a chemical that just happens to activates this sensor. Plants have it to ward off predators. Joke’s on the plants.
For more detail, those heat sensors are called TRPV channels and they locate on pain neurons. On exposed flesh and mucous membranes TRPV’s are also sensitive to acid and salt to a degree. Textbook answer for spicy is that it’s caused by an oil called capsaicin but it’s actually a family of capsaicinoids that might contribute to the different kinds of heat you’d get from jalapenos vs habaneros vs black pepper etc
[Capsaicin](https://en.wikipedia.org/wiki/Capsaicin) produced by the various spicy plants (peppers, etc.) causes the burning sensation, and also an inflammation (swelling, tenderness). You just have taste buds that react to it to sense as “spicy”. It’s an oil, so it doesn’t dissolve in water very well; milk works because it has fats in it that can dissolve the capsaicin and take it away from your mouth / tongue.
The reciprocal substance is [Menthol](https://en.wikipedia.org/wiki/Menthol), which produces a sensation of cool, and also numbs pain and soothes the tissue. Menthol is produced by the mint plants.
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