Ringworm of the skin usually causes a very itchy rash. It often makes a pattern in the shape of a ring, but not always. Sometimes it is just a red, itchy rash.
If you have a ring-shaped rash, you very likely have ringworm. Your doctor will be able to tell for sure. He or she will probably look at a scraping from the rash under a microscope to check for the ringworm fungus. Read more about the diagnosis and treatment of ringworm.