Bad breath should be registered with stomatology and gastroenterology. The appearance of bad breath is related to oral diseases as well as digestive system diseases, so you need to choose the department according to different causes. For patients with bad breath caused by gingivitis, periodontitis, and dental caries, they need to go to the stomatology department for treatment of oral diseases. Insufficient gastric power in the digestive system, food stagnation in the stomach for a long time, food spoilage, fermentation will produce a bad smell and emit through the esophagus, which will also cause bad breath, this case should choose gastroenterology. Gastroenterology in the treatment of bad breath, mainly to restore the peristaltic function of the stomach, to promote the digestion of food in the stomach, the treatment period also need to avoid eating spicy, greasy food, otherwise it will affect the effectiveness of treatment. In addition, H. pylori infection may also cause bad breath, which can be detected by doing a carbon 13 or 14 breath test.