Destroys precancerous and cancerous cells: 5-FU selectively targets rapidly dividing atypical cells in the skin. When applied to areas with sun damage, it causes a reaction that erodes actinic keratoses and superficial basal or squamous cell carcinomas. Over a few weeks of use, lesions crust and flake off, replaced by new healthy skin. Post-treatment, clinical studies show smoother, younger-looking skin due to the removal of dysplastic cells and sun-damaged collagen. It’s a gold-standard field therapy for sun-induced skin damage (with the side effect of temporary redness and irritation during treatment).