Mouth ulcers may be caused by external stimuli, lack of vitamins, mental factors or oral diseases. 1. External stimuli: for example, lips encounter hot food or water, teeth or external external forces and lead to lip breakage, there will be damage to the oral mucosa, the formation of oral lip ulcers. 2. Lack of vitamins: due to partiality, picky eating, do not love to eat fresh vegetables and fruits, resulting in the lack of vitamins and trace elements in the body, can also lead to mouth ulcers. 3. Mental factors: if the mental stress is relatively large, excessive mental tension, it will lead to the body’s immune function decline, susceptible to viral infections, which will lead to mouth ulcers. 4. Oral disease: If there are caries, periodontitis, wisdom teeth pericoronitis or bad restorations in the mouth, these inflammations will lead to an increase in disease-causing bacteria in the mouth, and if the bad restorations can often scrape or bite the mucous membranes, it will also lead to ulcers. Mouth ulcers may also have other causes, it is recommended to go to the hospital in a timely manner, improve the examination to clarify the cause of the disease, to give targeted treatment or treatment.