Some mouth ulcers are oral cancer. Frequent mouth ulcers are a common disease in the oral mucosa department, mostly seen in the elderly and children who have poor body resistance. Lack of trace elements in the body, such as iron deficiency will lead to increased brittleness of the mucous membrane and traumatic ulcers will appear when biting the lips. Vitamin B and vitamin C deficiencies also tend to induce mouth ulcers. Genetic factors or viral infections are also triggers for recurrent mouth ulcers. The ulcer usually heals itself in about two weeks, and after it heals, it will recur in its original position. This kind of ulcer is also called recurrent aphthous ulcer, and the chance of cancer is relatively small. If the ulcers are caused by local irritation, such as residual crowns or sharp tooth tips, or single large and deep ulcers, and if the ulcers have irregular changes and do not heal for more than two weeks, or if they do not heal for a long time, they have a higher chance of becoming cancerous. Early biopsy can be performed. It is necessary to promptly remove the residual crown and root, sharpen the tip of the tooth, and remove the external irritants. Therefore, if oral ulcers do not heal in two weeks or if local irritants are not removed in time, they may become cancerous and should be examined in a dental hospital as soon as possible.