Bitter corners of the mouth are caused by oral infections, digestive system diseases, kidney diseases and so on. 1. Bitter mouth caused by oral infection: common periodontitis, gingivitis, gingivitis, lingual inflammation, oral ulcers and so on. 2. Bitter corners of the mouth caused by digestive system diseases: common diseases include gastrointestinal dyspepsia, bile reflux gastritis and esophagitis, cholecystitis, gallstones, hepatitis and so on. 3. Kidney diseases: common diseases include nephritis, renal insufficiency, etc., which can cause bitter mouth and dry mouth symptoms. The symptoms of bitter corners of the mouth, you need to go to the hospital for relevant examinations, such as oral examination, gastroscopy, etc., to identify the cause of the disease, and actively cooperate with the doctor to carry out targeted treatment; in addition to improve the bad habits, eat more fresh fruits and vegetables; and actively carry out oral hygiene and care.