The reason why mouth ulcers are always bad may be the following: First, the lack of vitamins and trace elements in the body caused by the lack of b vitamins, vitamin C, or iron and zinc in trace elements in the body, are likely to make mouth ulcers recurring. Second, incorrect eating habits caused by the preference for spicy, irritating food, food with too high a temperature, these physical and chemical stimuli will directly stimulate the mucosa, resulting in repeated ulcers do not heal, and even recurrent ulcers. Third, the immune function disorder or extremely low caused by, this kind of people can take the appropriate amount of drugs to improve the immune function, such as thymidine and pidomod. Fourth, the mouth is suffering from dental diseases, such as too sharp tooth tip, root, crown, bad restoration, etc. These can often bite and scrape the mucous membrane inside the mouth, but also make the mucous membrane recurrent, traumatic ulcers.