Look a little closer
Eating chili does not raise the mouth's temperature to the level of a flame. Capsaicin molecules directly activate nerve pathways that detect damaging heat, sending the brain a convincing signal that heat is present.
One key pathway is the TRPV1 ion channel on sensory nerve endings. It opens in response to high temperatures and acidic conditions, but capsaicin can open it too. Charged ions then enter the cell and start a nerve signal.
Spiciness is therefore different from basic tastes such as sweet, salty, sour, bitter and umami. It belongs to chemesthesis: the trigeminal system's detection of chemical irritation, temperature and pain in the mouth and nose.
The body may respond as if heat were real. Flushing, sweating and a runny nose help release heat or wash away irritation, but the sensation alone does not prove that the food or body became dramatically hotter.
Capsaicin associates better with fats than with water, so a sip of water may not remove it effectively from the mouth. Foods containing fat and protein, including dairy products, can help disperse it.
Repeated exposure can make some people less sensitive, although responses vary widely. Chili's 'fire' is not thermometer heat but a chemical signal borrowing the nervous system's heat-detection circuit.
