Frequent oral ulcers are called recurrent aphthous ulcers, whose specific etiology and pathogenic mechanism are not clear, and may be related to immune factors, genetic factors, environmental factors, etc., as follows. 1. Immune factors: it may be related to abnormal T-cell-mediated immune response, abnormal humoral immunity, autoimmunity and so on. 2. Genetic factors: patients with recurrent aphthous ulcer may have certain pathological genetic qualities and abnormalities of genetic material. 3. Environmental factors: including psycho-neurological constitution, psychological and behavioral status, working life and social environment. The occurrence of recurrent Aphthous ulcer may also be related to other factors, it is recommended to go to the hospital in time to receive early professional treatment.