Stratum Corneum- Provides mechanical protection, impermeability, and barrier to water loss
- Brick and mortar model: lipid-depleted, protein-rich corneocytes (“bricks”) surrounded by extracellular lipid-rich matrix (“mortar”)
- Corneocytes composed of high weight keratins embedded in filaggrin-rich matrix
- Urocanic acid (UCA): filaggrin degradation product found naturally in the cornified layer; absorbs/blocks UV radiation and forms natural moisturization factor (NMF) with other filaggrin degradation products (amino acids, pyrrolidone carboxylic acid); NMF allows stratum corneum to remain hydrated even in drying conditions
- Ceramide is a major lipid barrier of skin; other barrier lipids include cholesterol, cholesterol sulfate, and fatty acids
| | | | | | Of note, steroid sulfatase cleaves cholesterol sulfate to cholesterol; enzyme abnormal in X-linked ichthyosis, resulting in more cohesive corneocytes | | | | | |
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