Chilli isn't hot: capsaicin trips the heat alarm on your tongue

A chilli is exactly as warm as the room. There is no heat in it at all.

The burn comes from capsaicin, a molecule that pries open TRPV1, the gate in your nerves that normally opens only above about 43 °C. Your brain gets the same "you're being scalded" signal real heat sends, so you sweat and flush over a fire that isn't there.

Below: fool the gate yourself, see why water fails and milk works, and why birds eat the hottest peppers without flinching.