Mouth ulcers always recurring may be caused by irregular diet, mental stress, oral diseases and other reasons. 1. Irregular diet: eating spicy and stimulating food, smoking, drinking or not eating fresh vegetables and fruits for a long time, leading to the lack of vitamins, calcium, iron, zinc and other trace elements in the body, may produce mouth ulcers. 2. Mental stress: long-term high mental tension, anxiety and other emotions, may cause the body to stress reaction, the body’s resistance to decline, easy to produce mouth ulcers. 3. Oral diseases: such as the presence of untreated dental caries, residual roots and crowns, poor restorations or sharp tips and other occlusal trauma, is also a major factor in inducing mouth ulcers. Stubborn mouth ulcers may also be caused by other reasons, if the patient appears to mouth ulcers always recurring situation, it is recommended to seek medical attention in time, under the guidance of the doctor, to take the appropriate treatment program.