Capsaicin (8-methyl-N-vanillyl-6-nonenamide) is an active component of chili peppers, which are plants belonging to the genus Capsicum. It is a chemical irritant and neurotoxin for mammals, including humans, and produces a sensation of burning in any tissue with which it comes into contact. Capsaicin and several related amides (capsaicinoids) are produced as secondary metabolites by chili peppers, likely as deterrents against certain mammals and fungi. Pure capsaicin is a hydrophobic, colorless, highly pungent crystalline solid.

Chili peppers, also spelled chile or chilli, are varieties of the berry-fruit of plants from the genus Capsicum, which are members of the nightshade family Solanaceae, cultivated for their pungency. Chili peppers are widely used in many cuisines as a spice to add "heat" to dishes. Capsaicin and related compounds known as capsaicinoids are the substances that give chili peppers their intensity when ingested or applied topically. Chili peppers exhibit a range of heat and flavors. This diversity is the reason behind the availability of different types of paprika and chili powder, each offering its own taste and heat level.