Sebaceous Glands

About the Sebaceous Glands

Sebaceous glands are small glands in the dermis that produce sebum, an oily mixture of triglycerides, wax esters, squalene, and free fatty acids. Most open into hair follicles, forming part of the pilosebaceous unit, and they are most numerous on the face, scalp, chest, and upper back, while being absent from the palms and soles. Sebum lubricates and waterproofs the skin and hair and contributes to the skin barrier. Sebaceous glands release their product by holocrine secretion, in which whole cells fill with lipid and then disintegrate. Their activity is driven mainly by androgens, which is why sebum production rises sharply at puberty. Some glands open directly onto the skin, such as the meibomian glands of the eyelids, which add oil to the tear film, and Fordyce spots on the lips. Overproduction of sebum together with blockage of follicles and the bacterium Cutibacterium acnes underlies acne vulgaris. Other conditions involving these glands include seborrheic dermatitis and sebaceous hyperplasia.