The sebaceous glands are glands found in the skin of mammals. They secrete an oily substance called sebum, that is made of fat (lipids) and the debris of dead fat-producing cells. It acts to protect and waterproof hair and skin. Sebaceous glands can usually be found in hair covered areas where they are contained in hair follicles, but they are also found in nonhaired areas of lips, eyelids, penis, labia minora and nipples. Sebaceous glands that are found in hair follicles deposit sebum on the hairs, and bring it to the skin surface along the hair shaft. At the hairless areas, sebum gets to the surface through ducts.

The sebaceous glands of a fetus in utero secrete a substance called Vernix caseosa, a "waxy" or "cheesy" white substance found coating the skin of newborn humans.

Sebaceous glands can be involved in skin problems (typically acne), which are studied and treated by dermatologists.

A blocked sebaceous gland can result in a sebaceous cyst.