Bitter mouth and also mouth ulcers are usually caused by oral infections, lowered immunity, poor diet and other reasons. 1. Oral infection: oral infection is generally caused by poor oral hygiene, may appear bitter mouth, loss of appetite and other symptoms, long-term recurrent infections that lead to mouth ulcers. 2. Reduced immunity: bitter mouth and mouth ulcers can also be caused by the patient’s reduced immunity, reduced immunity is usually caused by patients with malnutrition or lack of exercise, anorexia, fatigue, colds, mouth ulcers and other symptoms may occur. 3. Poor diet: If the patient long-term overeating or eating greasy food, it will increase the burden on the stomach and intestines, causing bile reflux, which causes bitter taste in the mouth, and long-term inattention to diet will lead to mouth ulcers. It is recommended that patients who are not feeling well go to the hospital in time to check under the guidance of the doctor for treatment, usually pay attention to oral hygiene, light diet, avoid spicy and stimulating food, eat more vegetables and fruits rich in vitamins, appropriate exercise to improve immunity, avoid staying up all night.