The cause of mouth ulcers in the mouth often long is not clear, may be due to heredity, body immunity, local factors, psychology, living environment factors, etc., it is recommended to go to the hospital for specific examination and treatment. 1. Mouth ulcers are genetically predisposed, mainly polygenic. 2. Low immune function is easy to grow mouth ulcers; T-cell subpopulation immunity dysregulation will also appear mouth ulcers. 3. Localized mechanical friction, e.g., over-pointed tooth edges, stumps, etc. 4. Patients with anxiety disorders may not rest well and are prone to ulcers. 5. Lack of nutrients in food, physical and chemical stimuli in the living environment, etc. may make mouth ulcers easily.