Skin barrier cross-section Cross-section of the skin on an office worker's hand: skin cells (bricks) sealed by natural oils (mortar). Alcohol sanitizer evaporates and strips the oils; moisture escapes and irritants get in. SURFACE · BACK OF THE HAND · AT THE DESK 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 Alcohol sanitizer

Brick-and-mortar model of the stratum corneum: Elias PM, J Invest Dermatol 1983;80:44s–49s. Exposure: R&R Lotion blog, The Side Effects of Hand Sanitizers (2022). Illustration for education only.