Cause 1: Patients suffering from systemic diseases and digestive system diseases are prone to oral ulcers, mainly by affecting the immune system and causing disease. Mouth ulcers are associated with gastric ulcers, duodenal ulcers, ulcerative colitis, restrictive enteritis, hepatitis, etc. Studies have shown that 30-48% of patients with mouth ulcers have digestive disorders such as bloating, diarrhea or constipation. More than 9% of them have peptic ulcers. Cause 2: Some female patients tend to occur during menstruation, which may be related to a decrease in the amount of estrogen in the body. Some women have mouth ulcers every time they have their periods or around the time of menstruation, which can only be temporarily relieved by medication and still appear as usual in the next month when they are menstruating, with unbearable pain, and at the same time, are often accompanied by annoying symptoms such as dry mouth, irritability, irritability and dry stools. Cause 3: Mental factors Some patients develop the disease under mental tension, mood swings, and poor sleep conditions, which may be related to plant nerve dysfunction. Cause 4: Genetic factors such as both parents suffer from recurrent mouth ulcer, their children about 80-90% of the disease, if one of the parents suffer from this disease, their children about 50-60% of the disease. Cause 5: Other factors such as lack of trace elements zinc, iron, folic acid, vitamin B12, malnutrition, etc., can reduce immune function and increase the likelihood of recurrent mouth ulcers.