Skin Barrier Function
The skin's ability to prevent water loss, resist environmental damage, and block entry of pathogens and irritants. Barrier function depends on the integrity of the stratum corneum, its lipid matrix, and tight junctions between keratinocytes. Compromised barrier function underlies many skin conditions.
Technical Context
Skin barrier integrity depends on three components: physical barrier (SC bricks-and-mortar structure — corneocytes, lamellar lipid matrix, cornified envelope), chemical/biochemical barrier (acidic pH 4.5-5.5 maintained by fatty acids and amino acids — the acid mantle; natural moisturising factors/NMFs — hygroscopic amino acids, urea, lactate derived from filaggrin degradation — maintaining SC hydration), and immunological barrier (antimicrobial peptides — defensins, cathelicidins/LL-37, dermcidin; toll-like receptors on keratinocytes detecting pathogens). Barrier disruption cycle: SC damage → increased TEWL → dehydration → inflammation → protease activation → further barrier degradation. Restoration: ceramide-dominant lipid replacement, NMF replenishment, pH normalisation, and allowing keratinocyte differentiation to rebuild normal SC. For peptide skincare research, barrier function assessment (TEWL, SC hydration by corneometry, and skin pH) provides objective endpoints for evaluating product effects.