Ringworm is an infection on the skin, hair, or nails. It's caused by a fungus. The infection usually causes a rash made up of round patches with raised, red edges. The rash spreads from the edges, often leaving the center clear. This ring shape is why it's called ringworm.
There are different types of ringworm. Depending on the type, it may be treated with prescription or over-the-counter antifungal medicine.