Sebaceous gland
Glandula sebacea
Definition
Sebaceous glands are holocrine exocrine glands found throughout the skin, most densely on the face and scalp, that produce and secrete sebum — a lipid-rich substance composed primarily of triglycerides, wax esters, squalene, and free fatty acids. These glands are typically associated with hair follicles, forming the pilosebaceous unit, though free sebaceous glands (not associated with hair follicles) exist on the lips, eyelids (Meibomian glands), and genitalia (Fordyce spots).
Structure and Function
Sebaceous glands are multilobulated structures composed of specialized sebocytes that accumulate lipid droplets as they mature. In the holocrine secretion process, the entire cell disintegrates to release its lipid contents into the sebaceous duct, which empties into the upper portion of the hair follicle canal. Key functions include:
Skin barrier maintenance — sebum forms a lipid film on the skin surface that helps prevent transepidermal water loss and maintains skin hydration
Antimicrobial defense — free fatty acids in sebum (particularly sapienic acid) have bactericidal and fungicidal properties
Thermoregulation — the lipid coating contributes to insulation and waterproofing of the skin surface
Immunomodulation — sebocytes express innate immune receptors (e.g., Toll-like receptors) and can produce antimicrobial peptides and pro-inflammatory cytokines
Regulation
Sebaceous gland activity is primarily regulated by androgens, particularly dihydrotestosterone (DHT), which stimulates sebocyte proliferation and lipogenesis. This explains the surge in sebum production during puberty and the role of androgen excess in conditions such as acne vulgaris. Other modulators include insulin-like growth factor 1 (IGF-1), peroxisome proliferator-activated receptors (PPARs), and neuropeptides.
Clinical Significance
Dysfunction of sebaceous glands is central to several dermatologic conditions:
Acne vulgaris — excess sebum production combined with follicular hyperkeratinization and colonization by Cutibacterium acnes
Seborrheic dermatitis — altered sebum composition and Malassezia colonization
Sebaceous hyperplasia and sebaceous adenoma — benign proliferative conditions; multiple sebaceous neoplasms may suggest Muir-Torre syndrome (a variant of Lynch syndrome)
Sebaceous carcinoma — a rare but aggressive malignancy, most commonly arising on the eyelid
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