Capsaicin, also known as capsaicin, is the active ingredient of pepper, which is irritating to mammals including humans and can cause burning sensation in the mouth. Capsaicin and some related compounds, also known as capsaicin, may be secondary metabolites produced by pepper to prevent herbivores from eating and fungi parasitism. Generally birds are not sensitive to capsaicin. Pure capsaicin is a hydrophobic, lipophilic, colorless and odorless crystalline or waxy compound.
Capsaicin is the main capsaicin in pepper, and dihydrocapsaicin ranks second. These two compounds are almost twice as hot as nordihydrocapsaicin, homodihydrocapsaicin and homocapsaicin.