Castoreum

Castoreum 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. The castor sacs are not true glands (endocrine or exocrine) on a cellular level, hence references to these structures as preputial glands or castor glands are misnomers.

In perfume-making, the term castoreum is more liberally applied to denote the resinoid extract resulting from the dried and alcohol tinctured beaver castor. The dried beaver castor sacs are generally aged for two or more years to mellow and for their raw harshness to dissipate. Some classic perfumes incorporating castor are Emeraude, Coty, Chanel, Cuir de Russie, Magie Noire, Lancôme Caractère, Hechter Madame, Carven, Givenchy III, Shalimar, and many "leather" themed compositions.

Although modern medical use of castoreum is rare, the dried pair of scent glands (the "castors") may still be worth more than a beaver pelt itself. Castoreum appeared in the materia medica until the 18th century, used to treat many different ailments, including headache, fever, and hysteria.

In the United States, Castoreum has been approved by the Food and Drug Administration (FDA) as a food additive, often referenced simply as a "natural flavoring" in the product's list of ingredients. It is commonly used in both food and beverages, especially as vanilla and raspberry flavoring.