Mouth ulcers for a month are not well related to long-term improper diet, emotional fluctuations, etc., but also consider recurrent aphthous ulcers, white plug syndrome, oral cancer. 1. Dietary and emotional factors: for some patients with long-term improper diet, such as the intake of spicy and stimulating foods, allergic foods, etc., it is easy to have mouth ulcers for a month. Some patients should also be vigilant is caused by mental tension, mood swings and other factors. 2. Recurrent aphthous ulcers: the etiology is still unclear, may be related to immune factors, genetic factors, psychological factors. Patients commonly manifested as recurrent, isolated round or oval superficial ulcers, also can be accompanied by pain, fever, mouth ulcers for a month are not good. 3. Leukoarai syndrome: the cause of the disease is not clear, may be related to genetic factors, pathogen infection. Leukoarai syndrome will cause recurrent oral and genital ulcers and skin damage, and some patients will have mouth ulcers for a month. 4. Oral cancer: oral cancer can cause mouth ulcers in some patients for one month. The occurrence of oral cancer is related to long-term smoking, drinking, chewing betel nut, viral infection and heredity, etc. Typical symptoms of patients include nodules, lumps and mucous membrane ulcers in the oral cavity, which are easy to be accompanied by pain, numbness, difficulty in speaking and enlarged lymph nodes in the local area. It is recommended that people with mouth ulcers that have not healed for a month should seek medical examination in order to clarify the cause of the disease and then follow the doctor’s instructions for treatment.