Light micrograph of the dermatophyte fungus Trichophyton tonsurans, a cause of ringworm. Ringworm, also known as tiniea, is a skin infection that causes a rash with severe itching. It can occur anywhere on the body and may be caused by various fungi, including Microsporum and Trichophyton. T. tonsurans is the main cause of ringworm of the scalp (tinea capitis).