Sebaceous

Sebaceous refers to sebum or to the sebaceous glands, the oil-producing structures of the skin. In humans, sebaceous glands are small, branched alveolar glands typically associated with hair follicles, forming part of the pilosebaceous unit. They are distributed over most of the body but are particularly numerous on the face and scalp; they are generally absent from glabrous skin such as the palms and soles. The eyelids contain modified sebaceous glands known as Meibomian glands, which contribute to the tear film.

Sebaceous glands secrete sebum, a lipid-rich substance consisting of triglycerides, wax esters, squalene, and cholesterol esters. Secretion occurs via holocrine mechanism: mature sebocytes accumulate lipids, then rupture to release sebum along with cell debris into the hair follicle canal or onto the skin surface. Sebum acts to lubricate and waterproof the skin and hair and provides some antimicrobial protection.

Hormonal regulation, particularly by androgens, influences sebaceous activity. Sebum production can change with age, hormones, and environmental factors, contributing to variation in skin oiliness.

Clinical relevance includes conditions such as acne vulgaris, where increased sebum production and follicular changes contribute to inflammation. Other issues involve sebaceous hyperplasia, sebaceous adenomas, and sebaceous gland carcinomas, though these are relatively uncommon. Meibomian gland dysfunction is a related condition affecting the eyelids and tear film. Understanding sebaceous biology helps in the management of oily skin, acne, and related disorders.