Mouth ulcers not only cause some pain to the organism and affect eating, but also affect normal work and study. Usually, mouth ulcers are caused by viral infections, autoimmune conditions, digestive system diseases, and nutritional deficiencies. 1, viral infection: mouth ulcers are mostly caused by herpes virus infection. Usually the ulcer surface in this case is relatively large, it is recommended to control the ulcer surface by taking antiviral drugs and anti-inflammatory drugs to achieve the purpose of healing. 2, autoimmune situation: patients with immune cells and non-immune cells between the coordination of dysfunction, will lead to ulcers in the mouth. Usually this situation is treated with drugs. 3, digestive system diseases: if the body gastrointestinal tract digestion is not good, easy to eat in the gastrointestinal tract when the accumulation of digestive system problems, resulting in oral ulcers. 4, nutritional deficiencies: If the body is picky about food for a long time, it is easy to lead to a lack of some trace elements in the body such as iron, calcium, magnesium, etc., resulting in a decline in immunity, which leads to ulcers in the mouth. 5.For the same ulcer that does not heal for a long time (no improvement for at least 2 weeks), we should be alert to the occurrence of oral cancer. Usually, patients with mouth ulcers are caused by the above-mentioned reasons, and it is recommended to take treatment according to the size of the ulcer surface and strengthen life care at the same time.