- Sebaceous glands are small, exocrine glands found in the dermis of the skin, closely associated with hair follicles. These glands are responsible for secreting sebum, an oily, lipid-rich substance that lubricates the skin and hair, providing essential protection and maintaining skin barrier integrity.
- Sebaceous glands are found throughout nearly all areas of the skin, except on the palms of the hands and soles of the feet, with high concentrations on the face, scalp, chest, and upper back.
- Sebaceous glands typically empty their contents into the hair follicle canal, forming a pilosebaceous unit along with the associated hair follicle and arrector pili muscle. However, in certain areas such as the lips, eyelids (Meibomian glands), areolae, and genitalia, sebaceous glands can open directly onto the skin surface. The glands are composed of sebocytes, specialized cells that produce sebum through a unique process known as holocrine secretion, where the entire cell disintegrates to release its lipid contents into the duct.
- Sebum is a complex mixture of triglycerides, wax esters, squalene, and free fatty acids. Its primary function is to moisturize the skin and hair, prevent water loss, and form a protective barrier against external irritants, bacteria, and fungi. Sebum also contributes to the slightly acidic pH of the skin surface (the “acid mantle”), which is important for microbial defense and epidermal health. Sebum production begins in the fetal period but increases dramatically during puberty due to rising levels of androgens, especially testosterone and dihydrotestosterone (DHT).
- The activity of sebaceous glands is under hormonal regulation, with androgens stimulating sebum production and estrogens exerting an inhibitory effect. This hormonal influence explains why sebaceous activity is minimal in childhood, peaks in adolescence and early adulthood, and declines with age. Overproduction of sebum can lead to oily skin, clogged pores, and the development of acne vulgaris, a common skin disorder particularly during puberty. Acne is caused by the hyperactivity of sebaceous glands, excessive sebum, abnormal keratinization, bacterial colonization (especially Cutibacterium acnes), and inflammation.
- On the other hand, hyposecretion of sebum can result in dry, flaky skin and is often associated with aging or certain dermatological conditions such as eczema and seborrheic dermatitis. Disorders of the sebaceous glands can range from benign tumors (like sebaceous hyperplasia) to rare conditions such as sebaceous gland carcinoma, which is more common in the glands of the eyelids.
- Sebaceous glands also have a role in innate immunity, as some of the lipids in sebum possess antimicrobial properties. Recent research has shown that sebocytes can also produce cytokines and antioxidants, indicating that these glands may participate in inflammatory regulation and skin immune responses.
- In dermatology and cosmetology, sebaceous gland function is a major consideration. Treatments for conditions like acne may involve retinoids, which normalize follicular keratinization and reduce sebum production, or hormonal therapy to modulate androgen effects. Isotretinoin, a powerful retinoid, is known to dramatically reduce sebaceous gland size and function, offering effective relief for severe acne.
