Pilosebaceous

Pilosebaceous describes the pilosebaceous unit, the skin structure that includes a hair follicle, the associated hair shaft, the sebaceous gland, and the arrector Pili muscle. The hair follicle anchors the hair and undergoes growth through the anagen, catagen, and telogen phases. The sebaceous gland, typically attached to the upper portion of the follicle, secretes sebum into the follicular infundibulum by holocrine secretion, lubricating hair and skin. The arrector pili muscle, a small smooth muscle, attaches to the follicle and can elevate the hair.

Sebaceous glands are strongly influenced by androgens; sebum production increases during puberty and varies with hormonal status. The pilosebaceous unit is most dense on the face and scalp and is absent in thick skin such as palms and soles. Sebum provides lubrication and contains antimicrobial lipids, but excessive production or follicular obstruction can contribute to acne and other inflammatory processes around the hair follicle.

Clinical relevance includes acne vulgaris, in which increased sebum, abnormal keratinization, and bacterial colonization by Propionibacterium acnes (Cutibacterium acnes) drive lesion formation such as comedones and inflammatory papules. Other disorders involve sebaceous hyperplasia and sebaceous adenoma, and hidradenitis suppurativa, which can reflect follicular occlusion and sebaceous gland involvement in apocrine-bearing areas. The pilosebaceous unit thus plays a central role in skin lubrication, barrier function, and several common dermatologic conditions.