Long-term mouth ulcers may not be the precursor of any disease, but a type of mouth ulcers such as recurrent aphthous stomatitis, which may also be related to bad living habits or oral stump roots, stump crowns to stimulate the local mucosa and long-term braces, etc. After seeking medical advice to exclude several conditions, it can be considered as the precursor of certain diseases. Patients with long-term vitamin B deficiency and oral cancer do not have other obvious symptoms in the early stage, mainly manifested by long-term mouth ulcers that do not heal, and other manifestations will gradually appear only when the condition worsens. 1. vitamin B deficiency: as the condition progresses, other symptoms such as foot fungus or plant nerve dysfunction may appear in addition to long-term mouth ulcers; 2. oral cancer: if the patient, in addition to long-term mouth ulcers, may also If the ulcer surface gradually expands and conventional treatment is ineffective, and in serious cases, there are even lumps, nodules and repeated bleeding without obvious reasons in the oral cavity, the patient should go to hospital for examination to clarify the cause and let the doctor judge whether it is oral cancer. There is another situation that long-term oral ulcers may be the clinical manifestation of the development of certain diseases, rather than the precursor of diseases. For example, gastric ulcer, duodenal ulcer, ulcerative colitis and other digestive system diseases are prone to long-term oral ulcers because the mucosal ulcers affect the absorption of vitamin B. It is recommended to seek medical examination in time to actively treat the primary disease and improve the symptoms of long-term oral ulcers.