Bitterness inside the mouth, to consider whether it appears in the near future or has been there for a long time, mainly seen in the following cases: First, abnormal living habits, eating habits: If it appears in the near future, to consider whether there are relevant living habits, eating habits abnormal in the near future, such as recent excessive smoking, drinking alcohol, as well as the recent existence of late night, overeating, or recently have some other bad habits, to Note that there may be the above-mentioned causes. Second, oral lesions: If the mouth has been bitter for a long time, you can consider whether the mouth is bitter due to abnormal oral infection, chronic inflammation, chronic mumps, chronic pharyngitis, or gingivitis, periodontitis and other chronic inflammatory diseases. Third, indigestion: If bitterness in the mouth appears after meals, pay attention to whether it is caused by gastrointestinal digestive malfunction, such as gastric ulcer, gastritis, Helicobacter pylori infection and other causes of indigestion in the stomach, and the symptoms of bitterness in the mouth easily appear after eating. Fourth, biliary tract diseases: If the patient is suffering from morning mouth bitterness, that is, the mouth is more bitter in the morning, it is necessary to consider whether there are biliary tract problems at this time. Because biliary tract diseases, such as poor bile secretion and pylorus relaxation, can easily lead to bile reflux, which is especially likely to occur after falling asleep. After sleeping, the body will be in a lying position, and because of the gravity factor, bile may flow back to the mouth, thus causing the symptom of bitter mouth in the morning. Bile reflux may occur after eating, especially when lying in bed immediately after eating, which may also lead to increased bile reflux.