Bitter mouth can be caused by oral diseases, and some are related to digestive system diseases. 1. Oral diseases include caries, periodontal disease and periapical disease. Bitter mouth can occur when inflammation exists and can be improved by dental treatment or scaling. Other oral diseases such as burning mouth syndrome can also appear bitter mouth, there is no effective treatment, but may be related to systemic diseases, need to consult a doctor, for the treatment of the original disease. 2. There are taste buds on the mucosa of the tongue that sense bitterness. Damage to the taste buds can also cause a lowering of the threshold of bitterness, and the sensation of bitter mouth is obvious. 3. Gastrointestinal dyspepsia or liver and gallbladder diseases, bile reflux into the mouth will appear bitter mouth, may be related to cholecystitis, gallstones or cholangitis. There may be other causes of bitter mouth, you can go to the hospital for examination and treatment.