Ringworm is a contagious fungal infection of the skin that has nothing to do with worms.
It can be itchy, but it's not painful or dangerous. It's similar to the fungus that causes athlete's foot, jock itch, and toenail fungus. In young children it most often affects only the torso or scalp. They're usually crusty or scaly on the outside and smooth in the center. As the fungus grows the rings get larger.