Oral ulcers are a common oral mucosal disease, and according to statistics, about 20% of people often suffer from recurrent oral ulcers, which are round or oval in shape, with clear boundaries and a diameter of 5 mm or less. The ulcer is round or oval in shape, with clear boundaries and a diameter of 5 mm or less. The affected area has a distinct burning pain, and the course of the disease is limited, usually healing after 7-1/4 days, but it is prone to recurrence. The causes of mouth ulcers are complex, and some patients develop them due to stress, trauma, smoking cessation, menstruation, and food allergies. Some patients also suffer from recurrent mouth ulcers due to lack of some essential vitamins in their diet. Since there are no special tests for mouth ulcers, the diagnosis can only be made by relying on the typical symptoms of ulcers and the history of the disease. However, some researchers have shown that if conventional treatments are not effective, especially if the ulcer does not heal for more than 3 weeks, the presence of other disease factors should be considered. For example, chronic inflammatory bowel disease, immune disorders such as neutropenia, HIV infection, systemic diseases such as lupus erythematosus, or skin diseases may cause oral ulcers; the use of anticancer drugs in cancer patients and antithyroid drugs in hyperthyroid patients may also produce oral ulcers. In addition, if a single chronic ulcer does not heal for a long time, oral cancer should be suspected. In children with periodic fever, pharyngitis, hand, foot and mouth disease and infectious mononucleosis, oral ulcers can also appear as concomitant symptoms. Therefore, it is important not to be paralyzed when the oral ulcer disease is not cured for a long time. The cause should be identified as soon as possible so that timely and symptomatic treatment can be given.