Halitosis is the foul odor emitted from the mouth or other air-filled cavities such as the nose, sinuses, and pharynx, which seriously affects people’s social interaction and psychological health, and has been reported by WHO as a disease. Survey shows that the prevalence of halitosis in China is 27.5%. First, the cause of local oral disorders is the main cause of halitosis, but should not be ignored is that halitosis is often the oral manifestations of some serious systemic diseases, there are some organic disorders can also lead to halitosis. Second, classification 1, orogenic halitosis According to statistics, 80% to 90% of halitosis is from the oral cavity. In the oral cavity, there are untreated dental caries, residual roots, residual crowns, bad restorations, abnormal anatomy, gingivitis, periodontitis and oral mucosal disease, etc. can cause bad breath. Among them, dental caries and periodontal disease are the most common related diseases. Food residues and plaque often remain in deep cavities and under the overhang of bad restorations, and bacteria decompose through fermentation to produce bad odor. Pulp necrosis or septic pulpitis, untreated can also emit odor; periodontal disease patients are often accompanied by a large amount of tartar, plaque, periodontal pockets of bacterial fermentation to produce hydrogen sulfide, indole and ammonia, thus producing odor. In addition, periodontal abscesses and periodontal pockets overflowing with pus, mostly Staphylococcus aureus combined with periodontal pathogenic bacteria infection, will also emit a foul odor. The quality and quantity of saliva also play an important role. The decrease in the amount of saliva, the increase in organic components such as protein reduces the flushing and buffering effect of saliva, so that bacteria multiply and decompose organic components in saliva, gingival fluid and food residues, producing a large number of volatile sulfide, indole and other substances, causing bad breath. 2, non-oral halitosis oral adjacent tissue diseases such as purulent tonsillitis, chronic maxillary sinusitis, atrophic rhinitis, etc., can produce purulent secretions and odor; common clinical internal diseases such as acute and chronic gastritis, peptic ulcer acid odor; pyloric obstruction, advanced gastric cancer often appear smelly duck egg halitosis; diabetic ketoacidosis patients can exhale acetone gas, uremic patients exhale rotten apple The smell of rotten apples. In addition, leukemia, vitamin deficiency, heavy metal poisoning and other diseases can cause bad breath. 3, physiological bad breath hunger, consumption of certain drugs or onions, garlic and other irritating food, smoking, sleep due to reduced saliva secretion of a large number of bacteria decomposition of food residues may cause a short period of bad breath. In healthy people, bad breath may be caused by the increase and thickening of plaque on the back of the tongue due to poor oral habits and oral hygiene. Because of the large surface area of the back of the tongue, there are many papillae, furrows and depressions, which is conducive to the retention of bacteria, oral mucosa shedding epithelium, food debris, etc., acting as a “bacterial storage room”, which is conducive to the production of bad breath. Some studies have shown that there is a positive correlation between the degree of bad breath, the amount of volatile sulfide and the thickness and area of the tongue moss, with a closer relationship with the thickness of the tongue moss, and a reduction in volatile sulfide after removal of the tongue moss. This may be because the thicker the tongue, the more anaerobic environment is formed, the more favorable for the growth of anaerobic bacteria, and thus the more favorable for the production of volatile sulfide, leading to bad breath. In addition, there is also pseudo-bad breath, which means that the patient himself feels that he has bad taste in his mouth, but the test result is negative. It can be improved by explanation and psychological counseling. Third, prevention and control Regularly check whether there is periodontal disease, dry mouth or other diseases. Maintaining good oral hygiene, eliminating periodontal disease, and having regular scaling and cleaning by a dentist can effectively reduce bad breath. No matter what the main cause of bad breath, good oral hygiene is still the most important, brush your teeth twice a day and clean the gap between your teeth, if you have dentures, you must take them off at night to rest, and only wear them back the next day after cleaning, so that the elimination of bad breath are very helpful.