Answer: Capsaicin

When you eat a chili pepper and get rewarded with a face-flushing burning sensation in your mouth, you can thank the alkaloid compound capsaicin. The compound was first identified in the early 19th century and derives its name from the genus classification for peppers, Capsicum. It’s found in varying concentrations in the different varieties of chili peppers—ranging from just a trace in the mild pepperoncini pepper, popular in Italian cuisine, to so-spicy-they-can-be-dangerous peppers like the ghost pepper that has been specifically cultivated to be hundreds of times hotter than a jalapeno.

Not only does the amount of capsaicin vary wildly between pepper types, it also varies wildly within the peppers themselves. Pepper seeds have no capsaicin at all, the white pith that connects the seeds to the inner wall of the pepper has the highest concentration of capsaicin, and the actual meat of the pepper has a lower concentration than the pith. Given that scientists believe the primary function of the capsaicin is to discourage mammals from eating the peppers and crushing the seeds with their molars (pepper seeds are dispersed predominantly by birds who are not affected by capsaicin and lack molars to damage the seeds), it makes sense that the pepper plant evolved to concentrate the pungent capsaicin around the seeds.

In addition to its wide use as a culinary flavoring agent around the world, capsaicin is used in a wide variety of non-culinary applications such as an irritant in self-defense and crowd control sprays as well as an analgesic for pain control.