Mouth ulcer is a disease caused by multiple factors, mainly including: 1. digestive system diseases and digestive system dysfunction: mouth ulcer is correlated with gastric ulcer, duodenal ulcer and colonic ulcer. Research shows that 30%-48% of patients with mouth ulcers have digestive system diseases, such as bloating, diarrhea or constipation, etc.; 2. Changes in endocrine: Some female patients occur mostly during menstruation, which may be related to the decrease in the amount of estrogen in the body. Some women have mouth ulcers during or before and after menstruation, which can only be temporarily relieved by medication, usually accompanied by dry mouth, irritability or dry stools. Clinical research, the appearance of mouth ulcers during menstruation is mainly due to the increase in the level of progesterone in the body and the decrease in hormone levels; 3, mental factors: some patients in the case of mental tension, mood swings, poor sleep conditions, may be related to the dysfunction of the vegetative nerves; 4, genetic factors: both parents suffer from recurrent mouth ulcers, the probability of recurrent mouth ulcers in their children reaches 80% – 90%, and the incidence of recurrent mouth ulcers in one parent reaches 50%-60% for their children; 5. Other factors: deficiency of vitamins or trace elements, such as vitamin B12, zinc, iron, folic acid, etc., and low immunity caused by malnutrition may also cause the occurrence of mouth ulcers.