Corners of the mouth ulcers can be treated on their own. The most common cause of corners of the mouth ulcers is stomatitis. A short period of time with corners of the mouth ulcers can be treated by applying erythromycin on itself, and if the symptoms are significantly relieved within 1-2 days, reapplication can be done until complete recovery. If there is no effect after application, further examination and treatment by a doctor is required.