Bad breath is also known as bad breath and halitosis. According to a survey, one in four people in China suffer from bad breath or have suffered from bad breath. As people have more social interactions and demand for their own comfort, bad breath has increasingly become one of the symptoms of public concern. Many people think that bad breath is a minor problem, but it is not. There are many causes of bad breath, and it is even dangerous. Bad breath may be transient or pathological. A large number of studies have confirmed that 85% to 90% of bad breath comes from the oral cavity, bad breath in the mouth of patients with halitosis mainly from the tongue and periodontal disease, they provide a great living space for bacteria, so that a large number of bacteria in the oral cavity, bacteria in the degradation of food residues in the mouth produce sulfide, is the main source of oral odor. Untreated caries, bad restorations, food inclusions, obstructed teeth, oral ulcers, tumors, etc. in the mouth can produce odor due to bacterial accumulation and food residues. Meanwhile, bad breath in some people originates from other parts of the body, such as respiratory system, digestive system and metabolic abnormalities, which is a sign of disease and should not be ignored. For example, it has been found that some people with periodontal health also have bad breath, and studies have found that the prevalence of H. pylori infection is significantly higher in patients with bad breath than in subjects without bad breath. The cause of H. pylori odor is still unclear, there are several possibilities: 1, H. pylori has urease activity, can break down urea to produce ammonia, ammonia is a substance with a special odor. 2, because H. pylori is an important cause of gastritis, gastroduodenal ulcer. When the presence of this bacteria infection, the gastrointestinal function is impaired to varying degrees, which may lead to the retention of food in the gastrointestinal tract for too long, through the decomposition of other bacteria in the gastrointestinal tract corruption to produce a variety of foul-smelling gases. Certain diets such as garlic, onion, radish, as well as smoking, drinking or taking certain drugs can also cause temporary odor in the breath. Physiological bad breath is common when waking up in the morning, which is due to the reduced flow of saliva during sleep at night and the reduced activity of the mouth, which enhances the metabolic activity of bacteria and produces more odor, which can disappear after meals and brushing teeth, so there is nothing to worry about. The causes of bad breath can interact with each other, so to eliminate bad breath, a comprehensive examination must be conducted to identify the cause and take comprehensive measures for its source.