Sebum: Skin's Natural Oil – Composition, Functions & Clinical Relevance

Sebum is a complex lipid mixture secreted by sebaceous glands (holocrine glands associated with hair follicles, except on lips, eyelids, genital mucosa).

Composition

• Triglycerides (~41%), wax esters (~26%), squalene (~12%), cholesterol esters (~3%), free cholesterol (~1.5%), free fatty acids (~16%).
• Unique to humans: sapienic acid (C16:1 Δ6), a major fatty acid with antimicrobial properties.

Functions

• Barrier & hydration: Occlusive film reduces transepidermal water loss (TEWL).
• Antimicrobial: Free fatty acids (esp. sapienic acid) inhibit S. aureus, C. acnes; low pH (~4.5–5.5) maintains acid mantle.
• Photoprotection: Squalene and vitamin E scavenge UV-generated ROS.
• Thermoregulation: Lipid film reduces evaporative cooling.
• Pheromone/social signaling: Metabolites by skin microbiota produce individual odor signatures.

Clinical Correlates

• Excess sebum (seborrhea) → Acne vulgaris, seborrheic dermatitis.
• Deficient sebum → Xerosis, atopic dermatitis flare, impaired barrier.
• Sebaceous hyperplasia – Benign yellowish papules on forehead/cheeks (elderly).
• Sebaceous carcinoma – Rare, aggressive malignancy (eyelid most common).

Regulation

• Androgens (DHT via 5α-reductase) → ↑ sebocyte proliferation & lipid synthesis.
• Retinoids (isotretinoin) → ↓ sebaceous gland size/output (therapeutic for severe acne).
• Seasonal: Higher in summer; lower in winter.

Sebum is not merely "oil"—it is a dynamic, bioactive interface between host and environment.