If you scrape your skin, remember to disinfect it or it'll get infected.
Tips
grammar
A verb-result structure: 擦 (scrape) + 破 (break) + 皮 (skin). You can slot extra words in: 擦破了一层皮 (scraped off a layer of skin), 擦破点皮 (just a little scrape). Common minor-injury language.