The cause of mouth ulcers is not completely clear, but it is generally believed to be related to the following points: 1, immune factors, patients with frequent mouth ulcers have more or less certain immune deficiencies or immune suppression. 2, genetic factors, both parents or one often mouth ulcers, then their children are also susceptible to the disease. 3, nutritional factors, it is generally believed that patients with frequent mouth ulcers may lack of vitamins and trace elements in the body. The most important thing is that it is a good idea to have a good understanding of the situation. These are the causes of mouth ulcers.