Ringworm is a very common infection caused by a skin fungus, especially in warm, humid climates. It can occur on any part of the skin or scalp. A dermatologist may easily recognize ringworm by its ring-shaped rash. To confirm the presence of the ringworm fungus, they will probably look at a skin scraping under a microscope or perform a skin culture. Most cases of ringworm are treated with over-the-counter or prescription antifungal creams or ointments. If ringworm is not cured with topical medication or if it is widespread, the doctor may prescribe antifungal pills.