Mouth ulcers may be caused by nutritional deficiencies, endocrine disorders, mental factors, immune factors or certain diseases. 1. Nutritional deficiencies: when little or no food containing vitamin B1, B2, B12, or folic acid, zinc, iron, selenium, etc., mouth ulcers may recur due to nutritional deficiencies. 2. Endocrine disorders: some recurrent ulcers may be associated with sex hormone disorders, often occurring in female patients. 3. Mental factors: long-term mental stress, poor sleep, emotional fluctuations can also lead to the emergence of recurrent ulcers. 4. Immune factors: people with low immunity are also prone to frequent recurrence of mouth ulcers. 5. Certain diseases: when suffering from inflammatory bowel disease, celiac disease, leukemia, AIDS and other diseases may also lead to frequent ulcers. When mouth ulcers occur frequently without obvious causes, timely diagnosis and treatment should be made to avoid delaying the condition.