Bad breath is the 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 WHO has reported bad breath as a disease. The survey shows that the prevalence of bad breath in China is 27.5%. In Western countries, it is 50%. About 10%~65% of people worldwide have suffered from bad breath. Western medical name: halitosis. Other names: Oral odor. Affiliation: Department of Pentology – Stomatology. Site of origin: Oral cavity. The main cause: local diseases of the oral cavity Pathogenesis: local diseases of the oral cavity 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. According to statistics, 80% to 90% of bad breath 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 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 amount of volatile sulfide, indole and other substances, causing bad breath. The pathogenesis of halitosis: 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-like gas, uremic patients exhale the smell of rotten apples. In addition, leukemia, vitamin deficiency, heavy metal poisoning and other diseases can cause bad breath. Physiological bad breath Hunger, consumption of certain drugs or onions, garlic and other irritating foods, smoking, sleep due to reduced saliva secretion of bacteria decomposition of food residues, etc. may cause transient 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 is, 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. Self-examination (1) self-perception method (cover the mouth and nose with a hand, exhale, and then smell the exhaled gas for odor); (2) feedback from a close person: the feedback from relatives, friends or spouse to assess; (3) clinical test method: mainly includes the wrist test, plastic spoon test; (4) direct nasal test by a professional physician: it is one of the easier to perform and more accurate methods of objective evaluation of halitosis (4) direct nasal test by a professional physician: it is an easier and more accurate method of objective evaluation of bad breath. (5) Laboratory tests: chemical analysis (gas chromatography/mass spectrometry sulfide monitor, high performance liquid chromatography, zinc oxide thin film semiconductor sensor, BANA analysis), milk gargle oxygen depletion test, microbial and fungal detection, saliva culture, etc.; (6) Manual nasal: including portable sulfide determination, plastic spoon test, and the “nasal” test. Halimeter is a simple and easy-to-use method that uses the principle of chemical reaction to numerically indicate the ppb concentration of H2S in the mouth, but it is easily affected by other odors in the mouth, such as alcohol, volatile fragrance (perfume, hair styling agent, etc.). The electronic nose is a method to diagnose halitosis by identifying characteristic odors in the mouth of patients with halitosis, but its function has yet to be improved. Finding the cause of bad breath is not a terrible thing, but it can be treated if the cause is identified. The first consideration is whether the halitosis is of orogenic or non-oral origin, and for factors that cannot be ruled out in relation to halitosis, such as respiratory diseases (infection and necrosis of the nasal cavity, maxillary sinus, pharynx, lung), digestive diseases (gastritis, gastric ulcer, duodenal ulcer, gastrointestinal metabolic disorders, constipation, etc.), parenchymal organ damage (liver failure, renal failure) and diabetic ketosis, uremia, leukemia, vitamin deficiency, etc. These diseases should be treated locally or systemically first. If there are oral diseases that may cause bad breath, such as untreated dental caries, residual roots, residual crowns, defective restorations, gingivitis, periodontitis and oral mucosal disease, etc., timely medical treatment should be provided for dental caries, extraction of useless residual roots and crowns, removal of defective restorations, removal of incorrect anatomical structures, treatment of oral mucosal disease, and for patients with periodontal disease, basic treatment such as scaling and root scraping should be performed first, followed by systematic periodontal treatment and plaque control. For patients with periodontal disease, basic treatment such as scaling and root scraping is performed first, followed by systematic periodontal treatment and plaque control. Choose the correct brushing method, brush at least 2 times a day, and develop the habit of rinsing after eating. It is also very important to clean the tongue. Since 80% to 90% of bad breath is from the back of the tongue, the dentist should teach the patient to use a tongue scraper to clean the tongue properly. In vitro tests can also be performed to identify the patient’s main pathogenic bacteria, and topical antimicrobial rinses that effectively inhibit the growth of microorganisms on the tongue can be used. Nowadays, common mouthwashes include chlorhexidine, chlorinated compounds, hydrogen peroxide, sodium salts, zinc salts, etc. A good mouthwash should be able to maintain the ecological balance of normal oral flora and prevent new diseases caused by flora imbalance. Stimulate saliva secretion or use substitutes, as saliva has antibacterial, bactericidal, and oral cleansing effects, the treatment should also consider increasing the amount and flow rate of saliva, enhancing tongue movement, chewing fiber-rich food or chewing gum, etc. are conducive to reducing bad breath.