The main causes of mouth feeling bitter are as follows: 1, oral diseases: oral inflammation, such as gingivitis, gum bleeding can cause mouth feeling bitter. 2, stomach heat: like esophagitis, chronic gastritis, poor gastric power, the presence of bile reflux, heartburn symptoms, can cause mouth feeling bitter symptoms. 3, improper diet: resulting in stagnation of gastrointestinal function, eaten food in the gastrointestinal stay too long, easy to produce damp heat caused by mouth bitter, 4, chronic diseases: such as diabetes, tumor patients can also cause mouth feeling bitter. Chronic diseases: Patients with diabetes and tumors can also experience bitterness in the mouth, and liver and gallbladder diseases can also cause bitterness in the mouth, such as inflammation of the liver or gallbladder. 5. Work and life stress: Irregular life and poor sleep and rest can cause mental bitterness in the mouth.