The causes of perennial bad breath include physiologic and pathologic factors. Pathologic factors mainly include oral diseases, nasopharyngeal diseases, digestive diseases and other diseases. 1. Physiological factors, long-term smoking and drinking, poor oral hygiene habits, dry mouth may cause perennial bad breath. 2. Pathologic factors (1) Oral diseases. Such as dental caries, gingivitis, periodontitis, oral dryness, oral ulcers, oral cancer and so on. (2) Nasopharyngeal diseases. Such as atrophic rhinitis, chronic sinusitis purulent maxillary sinusitis, chronic pharyngitis chronic laryngitis. (3) Gastrointestinal diseases. Such as chronic gastritis, gastroesophageal reflux disease, dyspepsia and so on. Helicobacter pylori infection is a common cause. (4) Other diseases. Constipation, bronchitis, lung abscess, diabetes, chronic liver disease, etc. can also present with perennial bad breath. The specific causes of perennial bad breath need to be examined and diagnosed by a doctor in a regular hospital.