Cholesterol

Essential co-lipid of the stratum corneum (approximately 25% of SC lipids by mole fraction), required alongside ceramides and free fatty acids for lamellar body organization and long periodicity phase formation. A ceramide-dominant 3:1:1 molar ratio (ceramides:cholesterol:fatty acids) optimally accelerates barrier recovery, with FDA approval of a barrier repair emulsion using this ratio in 2006. Cholesterol alone cannot reconstitute barrier; equimolar trilipid combinations are required. Typical use level 2–3% in barrier formulations; dissolve in oil phase at elevated temperature.

Not FDA-restricted. An FDA-approved barrier repair emulsion employing the ceramide-dominant 3:1:1 molar ratio (ceramides:cholesterol:fatty acids) was approved in 2006 for dry-skin conditions. CIR reviewed; no safety concerns at cosmetic use levels (typically 2–3%). Essential co-lipid in healthy stratum corneum (approximately 25% of SC lipids by mole fraction).