Ringworm. Ringworm is a common skin infection that is caused by a fungus. It’s called “ringworm” because it can cause a circular rash (shaped like a ring) that is usually red and itchy. Anyone can get ringworm.The fungi that cause this infection can live on skin, surfaces, and on household items such as clothing, towels, and bedding.Ringworm goes by many names.t’s called “ringworm” because it can cause a circular rash (shaped like a ring) that is usually red and itchy. Anyone can get ringworm. The fungi that cause this infection can live on skin, surfaces, and on household items such as clothing, towels, and bedding. Ringworm goes by many names.