Castoreum /kæsˈtɔriəm/ is the exudate from the castor sacs of the mature North American Beaver (Castor canadensis) and the European Beaver (Castor fiber). Within the zoological realm, castoreum is the yellowish secretion of the castor sac in combination with the beaver's urine, used during scent marking of territory. Both male and female beavers possess a pair of castor sacs and a pair of anal glands located in two cavities under the skin between the pelvis and the base of the tail.
Today, it is used as a tincture in some perfumes and as a food additive.
Some classic perfumes incorporating castor are Emeraude, Chanel Antaeus, Cuir de Russie, Magie Noire, Lancôme Caractère, Hechter Madame, Givenchy III, Shalimar, and many "leather" themed compositions.
Castoreum has been traditionally used in Scandinavia for flavoring snaps commonly referred to as "Bäverhojt".