What Is Sebum?
Sebum is a complex mixture of lipids secreted by sebaceous glands (oil glands) embedded in the dermis, emptying into hair follicles. It is composed of triglycerides, wax esters, squalene, free fatty acids, and cholesterol esters. Sebum production is primarily regulated by androgens — which is why oil production increases significantly at puberty and varies across the menstrual cycle and with hormonal changes. The skin's surface receives sebum via the follicular canal, where it spreads across the surface to mix with sweat and form part of the acid mantle.
Functions of Sebum
Sebum plays several beneficial roles: it contributes to the skin's lipid film and partially supplements barrier function; it provides antimicrobial properties (fatty acids with activity against certain pathogens); it contributes to skin suppleness; and it is a precursor to the skin surface's acidic pH. Squalene within sebum is also a significant antioxidant. Despite its reputation as a problem substance, sebum is fundamentally a protective secretion.
When Sebum Becomes Problematic
Excess sebum production (seborrhoea), combined with follicular hyperkeratosis and C. acnes presence, creates the conditions for acne. Sebum oxidation — particularly of squalene under UV stress — generates comedogenic lipid peroxides that promote follicular plugging. Sebum composition changes in acne-prone skin: lower linoleic acid concentrations and higher levels of oxidised squalene are characteristic.
Oily skin myth: Stripping sebum aggressively with harsh cleansers triggers compensatory sebum overproduction, worsening oiliness. Balanced cleansing that removes excess without fully denuding the surface is more effective for long-term sebum management.
See Oily Skin Type and Acne Solutions.