The white material in a mouth ulcer is usually necrotic mucosal tissue, which is surrounded by a yellowish-white pseudomembrane and is accompanied by a burning sensation. Mouth ulcers are superficial ulcers that commonly occur on the mucous membranes of the mouth, most often on the inner lips and buccal mucous membranes. The ulcers are usually oval or round, covered with a yellowish-white pseudomembrane and surrounded by congestion and redness. The pain is severe during the attack, and in severe cases, it will affect the diet. Currently, the treatment of mouth ulcers is mainly based on medication, and the effect of medication varies from person to person due to large individual differences. Analgesic drugs such as lidocaine, anti-inflammatory drugs such as amoxicillin or ice boron powder are effective in the treatment of mouth ulcers, and in severe cases, immunosuppressants such as levamisole can be used, but these drugs should be used under the guidance of a doctor. Most mouth ulcers heal on their own, but if they recur, last a long time, or have serious symptoms, you should go to the hospital immediately.