Capsaicin is the active ingredient of pepper, which belongs to the genus Capsicum. It is an irritant to mammals (including humans), and can produce a burning sensation, and any tissue in contact with it will be irritated. Capsaicin and several related compounds are called capsaicinoids, which are secondary metabolites of pepper; they may be a deterrent to certain herbivores and fungi. Pure capsaicin is a hydrophobic, colorless, tasteless, crystalline to waxy compound.