Skin barrier cross-section Cross-section of the skin: the stratum corneum is made of flat dead cells (bricks) sealed by lipid mortar. Washing dissolves the mortar, water escapes and irritants enter. SURFACE · BACK OF THE HAND PHASE 1 · HEALTHY CROSS-SECTION, NOT TO SCALE Stratum corneum 10–20 layers of flat, dead cells.Your outer barrier. Lipid “mortar” Ceramides, cholesterol, fatty acidsseal the gaps between the bricks. Living epidermis Makes new cells that move up andflatten over about 4 weeks. Dermis Collagen and blood vessels. LEGEND Water Irritants

Brick-and-mortar model of the stratum corneum: Elias PM, J Invest Dermatol 1983;80:44s–49s. Illustration for education only.