There are many reasons for frequent mouth ulcers, such as autoimmune deficiency, malnutrition, systemic diseases, mechanical irritation and so on. 1. Decreased autoimmunity: Decreased autoimmunity can lead to easy breeding of bacteria in the mouth, which may cause frequent mouth ulcers. 2. Nutritional deficiencies: lack of vitamins and trace elements in the body can also cause frequent mouth ulcers. 3. Systemic diseases: duodenal ulcer, gastric ulcer, hepatitis, ulcerative colitis and other diseases, may also induce frequent mouth ulcers. 4. Mechanical stimulation: usually like to eat hard food, bad repair body, eat too fast and too fast, etc., may lead to mechanical stimulation, resulting in local damage, which induces frequent mouth ulcers. Frequent mouth ulcers are caused by many reasons, patients need to correct bad habits, and at the same time go to the hospital as soon as possible for examination, a clear diagnosis, give standardized treatment.