Ringworm is a fungus infection of the skin. It often shows on the scalp as round or oval patches of baldness or scaly skin. The circular patches usually spread along their outer borders while clearing at the center. The rash is sometimes shaped like a ring, which is why it’s called “ringworm.”

Sometimes the infected area is inflamed, reddened, crusty, and tender, with small swollen bumps. Ringworm is usually treated with medicines taken by mouth.