There is no special smell in the mouth of healthy people, but bad breath in the elderly is an abnormal phenomenon, which can be caused by oral diseases and systemic diseases. In addition to filling food residue and rotten odor, severe dental caries in the elderly can also cause infection, pus and bad odor in the periapical or adjacent tissues. When gum swelling, erosion, bleeding, pus overflow, tooth loosening, displacement or formation of swollen pus in periodontal disease patients, there will be bad smell in mouth. In the early stage of oral malignant tumor, except for local lumps or hard nodules, there may be no conscious symptoms. In the late stage, cancerous tissues continue to proliferate, the central part of necrosis and fall off, and local cauliflower ulcers, necrosis and infection occur, resulting in a special odor. Bad breath is caused by the fermentation of food residues left in the mouth due to bacterial action when teeth are not brushed or the mouth is not clean. In addition to the above oral diseases or local cause of bad breath, but also closely related to other systemic diseases, the ancestral medicine that “the stomach, water and grain, the spleen abundant transport. If the spleen and stomach dysfunction, digestion and absorption can not be carried out properly, food accumulation in the stomach, causing bad breath. There are a variety of bacteria in the human oral cavity, there is usually an interdependent, mutually-restrictive relationship between them, when the oral saliva is acidic, such bacteria are active, proliferation accelerated, halitosis, when the gastrointestinal tract disease, although the clinical symptoms vary, but can affect the digestion and absorption, the body’s material metabolism changes and then the oral cavity changes in acidity and alkalinity, conducive to corrosive bacteria The clinical symptoms are different, but they can affect the digestion and absorption, change the metabolism of substances in the body and thus the acidity and alkalinity of the mouth, which is conducive to the reproduction of corrosive bacteria and bad breath. Elderly diabetics, liver disease, chronic renal insufficiency, chronic bronchitis, emphysema patients, there will be a special smell in the mouth or bad breath. Regarding the prevention and treatment of halitosis, first of all, careful examination is necessary to clarify the diagnosis and then take appropriate treatment. Active treatment of oral diseases, including dental diseases, periodontitis, tonsillitis and other oral and pharyngeal mucosal diseases, can reduce bad breath. It is also important to rinse your mouth after meals, remove food residues adhering to your teeth and brush your teeth frequently to develop oral hygiene habits. People with bad breath are advised to quit smoking and drinking. As for those who have bad breath caused by systemic diseases, of course, lies in the control of the original disease.