Mouth odor bad breath phenomenon, mostly due to poor oral hygiene and caused by the failure to develop the habit of brushing teeth in the morning and evening and rinse after meals, or oral cleaning is not complete, so that food residues left on the surface of the teeth, food residues decomposition breeding bacteria, can cause bad breath. In addition to the reasons for poor personal hygiene, disease factors can also cause the mouth odor, the phenomenon of halitosis, common diseases include: 1, oral diseases: oral diseases and not treated in a timely manner, the aggravation of the disease will cause the mouth odor phenomenon, such as dental caries, gingivitis, periodontitis and other inflammatory diseases. Such diseases can lead to the growth of many bacteria in the mouth, the decomposition of anaerobic bacteria will produce sulfide, which will make the mouth smell of corruption, resulting in the mouth odor; 2, gastrointestinal diseases: exclude oral diseases caused by bad breath, but also may be caused by gastrointestinal problems, such as Helicobacter pylori infection, gastric ulcer, etc.. Damage to the gastric mucosa can cause functional indigestion, resulting in bad taste in the mouth and halitosis. In addition, constipation can lead to stool and gas in the intestines can not be discharged from the body in a timely manner, resulting in bad breath; 3, nasopharyngeal diseases: such as chronic pharyngitis, chronic sinusitis, tonsillitis, etc., when inflammation leads to increased secretions in the throat of patients, prone to anaerobic bacterial infection, resulting in bad breath; 4, systemic diseases: such as diabetes, renal failure, etc., the disease is not well controlled, can appear oral odor. Common diabetic ketoacidosis patients can appear in the mouth similar to the smell of rotten apple ketone odor, kidney failure patients can smell fish in the mouth, etc. In addition, the mouth odor will not only cause oral discomfort to patients, but also affect the patient’s mental health, affecting interpersonal communication. Therefore, it is necessary to maintain a good oral hygiene environment and actively treat the primary cause of bad breath to improve the symptoms of halitosis.