Ringworm infections on all parts of the body are caused by a group of fungi called dermatophytes, which includes several different species. Any of these parasitic species may colonize skin that is warm and moist. Dermatophytes live among the outer portion of the skin where they feed on the keratinized cells found in the upper layers of the epidermis.

Ringworm is highly communicable and can spread in several ways. It can be passed from person to person via direct, skin-to-skin contact with an infected person. Ringworm can also be passed to people by infected animals including dogs, cats, rabbits, goats, and horses. The fungi can also be spread by contact with object or surfaces that were touched by an infected person or animal or, in rare cases, by contact with infected soil.  If one part of your body is infected with the fungus that causes ringworm, it may spread from there to other body parts.