Sebaceous Glands

Sebaceous glands are the skin's oil glands. They produce sebum, a waxy, lipid-rich substance that lubricates and waterproofs the skin and hair. Most sebaceous glands open into a hair follicle, and together the gland, follicle, and hair form the pilosebaceous unit. Because they are tied to follicles, sebaceous glands are found over almost the entire body but are absent from the palms and soles.

Structure and Location

Each gland is made of rounded clusters called acini that connect to a common duct emptying into the follicle canal. The glands are most numerous and largest on the face, scalp, upper back, chest, and shoulders, areas prone to oiliness and acne. The cells that make oil are called sebocytes, arranged in layers within each acinus. At the outer (basal) layer sit germinative reservoir cells that divide and replace the gland; as new sebocytes mature, they move inward, fill with lipid, and eventually burst.

How They Work and Their Functions

Sebaceous glands use holocrine secretion, a distinctive process in which the entire sebocyte fills with oil, dies, and disintegrates to release its contents. This means the cell itself becomes the secretion. Sebum then travels up the follicle and onto the skin surface, where it provides roughly 90 percent of the skin's surface lipids. Functionally, sebum reduces water loss, keeps skin and hair supple, and has mild antimicrobial properties that help defend against bacteria and fungi. Sebaceous activity is strongly driven by androgens, which is why oil production surges at puberty.

Clinical Relevance

Overactive or blocked sebaceous glands are central to acne vulgaris, in which excess sebum combines with dead cells and bacteria to clog follicles. Excess sebum on the scalp contributes to seborrheic dermatitis and dandruff. Benign enlargement of the glands causes sebaceous hyperplasia, and clogged ducts can form sebaceous (epidermoid) cysts. This information is educational and not medical advice.