If the mouth is bitter before or after eating, it depends on whether it is before or after eating. If you have bitter mouth before meal, you should consider whether you have abnormal oral infection, gingivitis, periodontitis, mouth ulcer and so on, which cause bitterness of oral secretion. In addition, if there is bitterness in the mouth after meals, it is necessary to consider whether there is a factor of bile reflux, because bile belongs to bitterness, and food intake will lead to a large amount of bile secretion, especially when there is a disease of the biliary tract or a relaxation of the pylorus of the stomach, bile is easy to excrete abnormally and reflux through the relaxed pylorus into the stomach and into the mouth, causing the symptoms of bitterness in the mouth after meals. This is especially likely to occur when there is inactivity, sedentary or prolonged lying after a meal. At this time, it is important to pay attention to further prevention, including treatment of diseases, dietary habits, and improvement of living habits.