Bad breath is related to gastrointestinal diseases, throat diseases and oral diseases. There are a lot of gastrointestinal diseases, can lead to oral odor phenomenon, such as chronic gastritis, gastric ulcer, dyspepsia, etc., these diseases will lead to slow peristalsis of the stomach, food in the stomach and digestive juices to react, resulting in the taste of sour rot and emanate through the esophagus, especially in the stomach of Helicobacter pylori bacteria infected patients, the majority of oral cavity will be accompanied by the odor of the taste. Some people’s throat diseases belong to the purulent pharyngitis, will lead to the presence of a large number of purulent substances in the throat, thus leading to the oral cavity will appear to be foul-smelling. Some people’s oral odor is due to oral diseases, such as oral ulcers, gingivitis, periodontitis and other diseases are usually accompanied by bad breath, these diseases will lead to the gums contain rotting material, so it will emit a foul smell.