Ringworm is not a real worm. It's a common infection caused by a fungus. Ringworm goes by different names depending on where it is on your body. It's also known as jock itch and athlete's foot. When it's on your head, it's called tinea capitis. It causes patches of itchy skin and hair loss that may worsen over time. You also may get a painful, pus-filled sore called a kerion on your scalp.