辣椒素（英语：Capsaicin）又名辣椒碱，即反式-8-甲基-N-香草基-6-壬烯酰胺，分子结构式为(CH₃)₂CHCH=CH(CH₂)₄CONHCH₂C₆H₃-4-(OH)-3-(OCH₃，是辣椒属植物红辣椒的活性成分。它对包括人类在内的哺乳动物都有刺激性并可在口腔中产生灼烧感。辣椒素和与其相关一些的化合物并称为辣椒素类物质（英语：Capsaicinoids），它们可能是辣椒为阻止草食动物啃食和真菌寄生而产生的次级代谢产物。一般鸟类都对辣椒素类物质不敏感。纯的辣椒素是一种斥水亲脂、无色无嗅的结晶或蜡状化合物。

Capsaicin (/kæpˈseɪ.ᵻsɪn/ (INN); 8-methyl-N-vanillyl-6-nonenamide) is an active component of chili peppers, which are plants belonging to the genus Capsicum. It is an irritant for mammals, including humans, and produces a sensation of burning in any tissue with which it comes into contact. Capsaicin and several related compounds are called capsaicinoids and are produced as secondary metabolites by chili peppers, probably as deterrents against certain mammals and fungi. Pure capsaicin is a volatile, hydrophobic, colorless, odorless, crystalline to waxy compound.