Skin barrier cross-section Cross-section of the skin on a plant worker's hand: skin cells (bricks) sealed by lipid mortar. Oils coat the skin and a harsh solvent cleaner dissolves them along with the mortar; moisture escapes and irritants get in. SURFACE · BACK OF THE HAND · ON THE PLANT FLOOR 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 Oil Solvent cleaner

Brick-and-mortar model of the stratum corneum: Elias PM, J Invest Dermatol 1983;80:44s–49s. Exposure: R&R Lotion blog, The Do’s and Don’ts of Skin Care Products in Industrial Settings (2023). Illustration for education only.