There are many causes of bad breath, which can be divided into non-pathological bad breath and pathological bad breath. Pathological halitosis can be divided into dental caries, oral ulcers and other orogenic halitosis, atrophic rhinitis, diabetes and other non orogenic halitosis. 1. non-pathological bad breath: mainly related to the body intake of garlic, onion, radish and other foods, and smoking, not pay attention to oral hygiene and other factors. If recently taking dimethyl sulfide, quinine and antihistamines, etc., there may be a transient bad breath. 2. Pathologic bad breath. (1) oral halitosis: mainly due to oral diseases causing halitosis, common diseases are dental caries, oral ulcers, gingivitis, periodontitis, dental stumps, pulpitis, periodontal abscess and so on. (2) non-oral bad breath: atrophic rhinitis, diabetes mellitus, sinusitis, nasopharyngeal abscess, laryngeal cancer and Helicobacter pylori infection, acute and chronic gastritis, peptic ulcer, pyloric obstruction and other patients will have bad breath. For uremia, renal failure, leukemia, heavy metal poisoning, cirrhosis and other diseases, also bad breath. It is recommended that people with bad breath should strengthen oral care, brush teeth and rinse their mouths regularly. If accompanied by other uncomfortable symptoms or bad breath persists, it is necessary to consult a doctor in time.