More than ninety percent of the odor in the mouth is mainly caused by gingivitis periodontal disease. Periodontitis is the gathering of a large amount of plaque around the teeth, forming tartar, stimulating gum inflammation, manifested as red and swollen gums, easy to bleed, loose teeth, periodontal pockets overflowing pus, accompanied by oral odor is mostly malodorous. Other diseases in the oral cavity may also cause oral odor, such as dental caries causing inflammation and necrosis of the dental pulp will produce a corrupt odor, and other factors such as inappropriate treatment of bad fillings and bad dentures will make the area around the teeth unfavorable to clean, and plaque will gather and produce odor. Acute necrotizing gingivitis can produce putrid halitosis. Oral mucosal infection and mucosal erosion ulcer secondary infection can produce moderate halitosis, and some post-extraction wound infection can also cause bad breath. In addition, bad breath may also be a manifestation of systemic diseases such as gastrointestinal diseases. The treatment of bad breath is mainly directed at the cause of the disease, and some other measures can be taken to reduce bad breath, such as drinking more water, brushing teeth, rinsing mouth, using aromatic gargles, eating chewing gum, etc., but these methods can never replace the basic treatment of the disease causing bad breath.