The specific causes of oral ulcers are still unclear, with obvious individual differences, and may be the result of a single factor or a combination of factors, including immune factors, genetic factors, psychological factors, etc., as follows. 1. Immune factors: generally related to cellular immunity, patients may have a decline in cellular immune function and T lymphocyte subpopulation imbalance. 2. Genetic factors: studies on single gene inheritance, polygenic inheritance, genetic markers and genetic material of oral ulcers show that there is a certain genetic predisposition for the development of oral ulcers. 3. Psychological factors: tension, anxiety and other emotions, as well as long-term high-pressure state, mental stress on the development of oral ulcers have an impact. Mouth ulcers may also have other causes, it is recommended to go to the hospital to receive professional targeted treatment.