The causes of bad taste in the mouth can be broadly categorized into diseases of the gastrointestinal system and diseases of the oral system. 1. Gastrointestinal system diseases: Helicobacter pylori infection will appear in the mouth with odor symptoms, is the toxin produced by the Helicobacter pylori bacteria caused by the taste of the common diseases such as gastritis. If the patient has indigestion or constipation, there will also be abnormal odor in the mouth. 2. Oral system diseases: periodontitis, gingivitis patients due to inflammation problems, resulting in residual food residues in the mouth fermentation of the odor. You can clean your teeth and pay attention to oral hygiene care. If the patient’s mouth odor is recommended to the oral clinic or gastroenterology clinic for examination, to identify the cause, the cause of treatment, do not be careless.