Mouth ulcers, also known as canker sores, are common lesions that cause pain and discomfort in the mouth. They typically appear as small, white or grayish pits with red borders inside the cheeks, lips, gums, or tongue. The majority of people experience mouth ulcers at some point, which produce a burning sensation and make eating and swallowing difficult. While mouth ulcers usually heal within a week to ten days, it is important to treat them to alleviate pain and allow proper nutrition.