Sebum

Sebum is the waxy, lipid-rich substance produced by sebaceous glands in the skin that coats hair and the skin surface and helps keep it supple and water-resistant.

Sebaceous glands sit beside hair follicles across most of the body, most densely on the face, scalp, chest and upper back. Sebum is a mixture of triglycerides, wax esters, squalene and free fatty acids, and its production is driven by androgens, which is why output rises sharply at puberty and varies with hormonal cycles. It mixes with sweat and shed skin cells to form the surface film that limits water loss and supports the skin's resident bacteria.

Too much sebum, together with blocked follicles and bacterial growth, underlies acne, while too little contributes to dry, flaky skin. In dogs and cats, sebum keeps the coat glossy, and excessive or altered production shows as greasy, scaly or malodorous skin that veterinarians assess for underlying causes. Sebum output is measured in research with absorbent tapes or optical devices. Sebocytes express cannabinoid receptors, and cannabinoids have been studied for effects on sebum production in cell models; human evidence is early.