It's not a worm at all. It's a fungus that thrives in damp, warm places on and around your body: hair, nails, skin, floors, walls, clothes, and towels, for starters. The ring-shaped splotches of dry, itchy skin it causes can burn and sting. Ringworm is responsible for "athlete's foot" and "jock itch." Antifungal creams and pills help get rid of it, but sometimes it comes back in the same place.