Capsaicin is the primary compound in chili peppers responsible for their characteristic spicy, pungent flavor and burning sensation. It is a colorless, odorless compound produced by plants in the Capsicum genus, concentrated mostly in the membrane surrounding the seeds rather than in the seeds themselves.
Capsaicin was first isolated in impure form in 1816 by German chemist Christian Friedrich Bucholz; its chemical structure was worked out in 1919 by American chemist E.K. Nelson.
Heat is measured on the Scoville scale in Scoville heat units (SHU): bell peppers register near 0, while the hottest cultivated peppers (such as the Carolina Reaper and Pepper X) reach roughly 2 to 2.7 million SHU. Pure capsaicin itself measures around 16 million SHU, far hotter than any pepper.
Capsaicin is widely used across Mexican, Thai, Indian, and Szechuan Chinese cuisine, adding heat and depth to hot sauces, spice blends, and pickled foods.