Ringworm is a common fungal skin infection. Despite the name, it is not caused by a worm. It is caused by fungi called dermatophytes that can infect the skin, scalp, feet, groin, or nails. Ringworm can spread through direct skin contact, contaminated surfaces, shared personal items, pets, or damp environments. It is usually treatable, but some cases need medical evaluation, especially if the rash is spreading, recurrent, involves the scalp or nails, or does not improve. What