The specific cause of oral ulcers is unknown, the pathogenic mechanism is not clear, is the result of a combination of factors, including immune factors, genetic factors, etc., as follows. 1. Immune factors: mainly through the immune response to cause oral ulcers, may be related to cellular immune abnormalities, including T cell-mediated immune response abnormalities, humoral immune abnormalities and autoimmunity. 2. Genetic factors: Studies on single gene inheritance, polygenic inheritance, genetic markers and genetic material of oral ulcers show that the development of oral ulcers has a certain genetic tendency. The occurrence of mouth ulcers may also be related to other factors, if the symptoms of mouth ulcers are serious and prolonged, it is recommended to go to the hospital in a timely manner, and receive professional treatment as soon as possible.