Skin barrier cross-section Cross-section of the skin on a collection worker's hand: skin cells (bricks) sealed by lipid mortar. A harsh cleaner takes the grime off and wears the mortar thin; the skin cracks and grime and germs work in. SURFACE · BACK OF THE HAND · ON THE ROUTE 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 Grime and germs Grime Harsh cleaner

Brick-and-mortar model of the stratum corneum: Elias PM, J Invest Dermatol 1983;80:44s–49s. Exposure: R&R Lotion blog, Understanding Occupational Dermatitis and I.C. Hand Lotions (2023). Illustration for education only.