Learn about mouth ulcers, small sores that form on your gums, lips, tongue or inner cheeks. Find out what causes them, how to treat them and when to see a doctor. Mouth Ulcer Symptoms Causes and Effective Treatments A mouth ulcer, also known as a canker sore. It is a painful lesion that forms on the mucous membrane inside the mouth. It can occur on the gums, tongue, roof of the mouth, inner cheeks, or lips. These sores often appear as red, yellow, or white spots and can make eating, drinking, and speaking uncomfortable. Treatment typically involves topical medications to ease pain and promote healing, while maintaining good oral hygiene can help ... Mouth ulcers are common and usually harmless, but can be painful and uncomfortable. Learn how to treat them yourself, when to see a GP or dentist, and what to avoid to prevent them. Learn what causes mouth ulcers, how to prevent them, and when to seek medical help. Understand triggers like stress, injuries, diet, and health conditions.