The etiology of oral ulcers is still not clear, and is related to many factors, such as exertion, stress, trace element deficiency, etc. Zinc deficiency is also a causative factor for oral ulcers, but oral ulcers are not always caused by zinc deficiency. The etiology and pathogenesis of oral ulcers are still unclear, and the triggers may be mental stress, viral infections, excessive fatigue, vitamin or trace element deficiencies, local trauma, food, drugs, hormone level changes and so on. Oral ulcers are also a type of systemic disease, and immune, microbial, and genetic factors play a very large role in the occurrence and development of this disease. Micronutrient deficiencies (vitamin B12, zinc, iron, folic acid) can play a decreasing role in immunity and increase the incidence of mouth ulcers; bacterial infections such as Streptococcus haematobium and Helicobacter pylori are also very closely related to mouth ulcers. The appearance of mouth ulcers generally indicates that the organism may have systemic diseases, mouth ulcers and vitamin B absorption disorders, and duodenal ulcers, gastric ulcers, ulcerative colitis, hepatitis, restrictive enteritis, women’s menstruation, autonomic dysfunction disorders and so on are related. Therefore, attention should be paid to timely treatment.