There are many causes of bad breath, which include oral diseases, nasopharyngeal diseases, chronic gastritis and so on. Specific treatments include medication, surgery and so on. 1. Oral diseases: such as gum disease, oral mucosal lesions, etc., due to food residue for a long time in the oral cavity will produce chronic inflammation and even ulcers, thus causing bad breath. In addition to the treatment method of brushing teeth on time, compound chlorhexidine gargle solution gargle, if necessary, oral medication such as metronidazole. 2. Nasopharyngeal diseases: such as chronic rhinitis, sinusitis, pharyngitis, because there are often purulent secretions retained in the nasopharyngeal cavity is prone to recurrent infections, putrefactive bacteria produce a more foul odor, so sometimes the nasal cavity and mouth taste very bad. Treatment drugs include ephedrine, furosemide nasal drops, clavulanic acid and so on. If necessary, patients with chronic sinusitis can take puncture treatment. 3. Chronic gastritis: this type of patients may also cause bad breath, mainly due to poor digestion of food, long time in the stomach due to accumulation; in addition, pylori screw infection may also cause the above symptoms. Treatment drugs include Ranitidine, Magnesium Aluminum Carbonate, Mosapride, Aluminum Thioglycollate and so on. In addition to the above reasons, bad habits such as long-term smoking, not brushing teeth, or liver and kidney insufficiency, diabetic ketoacidosis, etc. can also cause bad breath. It is recommended to correct this bad habit and pay attention to oral hygiene. If the symptoms do not improve, or the bad breath is serious, it is recommended to go to the hospital for relevant examinations, under the guidance of the doctor for regular treatment and medication.