The causes of bad breath are generally the following: 1, the oral cavity itself, such as poor oral hygiene, gingivitis, periodontitis, dental caries, oral mucosal disease and other diseases; 2, nasopharyngeal problems, such as having chronic rhinitis, chronic pharyngitis; 3, respiratory problems, lung problems; 4, gastrointestinal tract diseases. If there are no problems in the oral cavity, nasal cavity, respiratory tract, and simply gastrointestinal tract diseases, the main check is for problems in this area of gastric disease, such as having chronic gastritis, functional gastrointestinal disease, which is prone to indigestion, acid reflux, belching, etc. Problems in this area should go for relevant examinations, such as gastroscopy to exclude whether there are organic lesions in the stomach, such as tumors, ulcers, etc. After the examination, the corresponding disease will be treated after a clear diagnosis is made. In addition, a test for Helicobacter pylori and a carbon 14 breath test can be done. If the test result is positive, it is necessary to eradicate H. pylori, and the stomach disease may be cured. This is because chronic gastritis, ulcers, and even other malignant lymphoma diseases of the stomach are associated with H. pylori.