Chemically there might as well be actual heat.
The spicy chemical (capsaicin) doesn’t activate taste buds, it activates the hot temperature receptors in your mouth.
So to your brain, it’s literally the exact same electrical/nerve signal coming in as if there *was* hot temperature in your mouth. There’s no way it can know that its hot-detectors were triggered by a funny chemical instead of heat. All it gets is the message “currently scalding = YES”. So you feel burning.
That’s also why hot temperature makes spicy food worse. Like a hot temp spicy soup. The heat and the spice combine to activate more burning receptors in your mouth more strongly than either factor would be itself, so the spicy soup feels *really* burning hot.
Latest Answers