Deficiency of vitamins and trace elements. Stomatitis can be triggered when there is a deficiency of trace elements such as zinc, iron, folic acid and vitamin B12. Many daily life behaviors may cause vitamin deficiency, such as over-rinsing rice, eating refined rice and noodles for a long time, and eating vegetarian food, which can easily cause B vitamin deficiency. High mental stress. Work exhaustion, mental stress, mood swings, neurological disorders, etc. can also make mouth ulcers repeatedly “visit”. Gastrointestinal diseases. An important reason why patients with gastrointestinal diseases are prone to mouth sores is that common diseases such as chronic gastritis, gastric ulcer, constipation, hemorrhoids, etc. affect the body’s absorption of vitamins. Effective treatment of gastrointestinal disorders is the “root cause” of recurrent mouth sores. Hormonal fluctuations. Some women develop mouth ulcers around the time of their period or menstruation, and they heal themselves or continue to have painful ulcers when they have their period the following month. This is mainly due to the increased level of progesterone and decreased level of estrogen in the body. Immune system disorder or immunodeficiency. Recurrent multiple mouth ulcers with or before and after external genital ulcers; acne and folliculitis on the skin; eye discomfort and vision loss should be considered leukoaraiosis. Lupus erythematosus may be the cause when oral ulcers are accompanied by hair loss, purplish red spots on the face and joint pain before and after the ulcers. If mouth ulcers are accompanied by persistent fever and frequent infections, hematologic disorders should be considered Tumors. Older patients with a longer history of oral ulcers should be alerted to the possibility of oral mucosal carcinoma if there are deeper and larger ulcers and unexplained lumps in the oral cavity.