The causes of mouth ulcers are more complex and include infections, autoimmune abnormalities and congenital dyskeratosis. 1. Infection: Infections that may cause oral ulcers include syphilis, tuberculosis, leprosy, fungal diseases and viral diseases. These germs and microorganisms attack the oral mucosa and cause destruction of the oral mucosa, which leads to the occurrence of oral ulcers. 2. Autoimmune abnormalities: systemic lupus erythematosus, leukemia, Reiter’s syndrome and other diseases due to autoimmune abnormalities are easily combined with oral and skin mucous membrane erosion, which can lead to chronic non-infectious oral ulcers. 3. Congenital dyskeratosis: congenital dyskeratosis makes multi-system involvement, in patients, skin, oral cavity, rectum and cervix are more malignant lesions, in which oral ulcers are characterized by the disappearance of tongue papillae, multiple white spots on the tongue, elliptical ulcerated surface, covered with a yellowish membrane, and peripheral congestion is obvious. The causes of mouth ulcers are complex, by their own conditioning mouth ulcers do not heal for a long time patients should go to the hospital in a timely manner to improve the examination, clear cause of the disease to give targeted treatment.