The reasons for bitterness in the mouth are mainly the following: 1st, it is the poor oral hygiene environment, because there is a large amount of food residue, soft scale and bacteria accumulated on the tooth surface and tongue surface, which will corrupt itself and lead to bitterness in the mouth; 2nd, it is because there are dental or periodontal diseases in the mouth, such as multiple teeth have dental caries, pulpitis, periapical inflammation, wisdom tooth pericoronitis, or large ulcers in the mucous membrane, leading to The third reason is that the body suffers from liver and biliary system and gastrointestinal digestive system diseases, such as bile reflux disease, cholecystitis, gallstone disease, due to the accumulation of bile and reflux into the mouth, it will cause the phenomenon of bitter mouth, in addition, if patients with indigestion or gastric power deficiency, due to the accumulation of food will also cause bitter mouth.