Why do spicy foods burn my tongue and make me sweat?

Chilli has got a molecule in it called capsaicin, and capsaicin locks onto a certain channel on the surface of nerve fibres in the mouth and all over the body that signal pain. When the capsaicin molecule from the chilli locks on tot hat nerve fibre, it activates the nerve. The same nerve fibres also signal temperature, so it fools the nervous system in to thinking that you're hotter than you are. This causes a heat reaction and is why you often get red and sweaty. The reason that water doesn't make it better is because capsicin dissolves in oil and doesn't mix with water. Putting water in doesn't make any difference as it stays locked onto the nerve cell. This is why you often get yogurt or yogurty drinks with spicy food, because they've got fat in them. If you want to get rid of it, you need something with some kind of fat in it. Alcohol will also dissolve capsaicin, so a slug of beer should help it to feel better.