A, the mouth emits foul odor, more stomach heat is partial Sheng 1, periodontitis, gingival overflow pus, oral erosion, carious gums along the food residue corruption fermentation, purulent tonsillitis, tonsil crypt at the accumulation of pus, etc., can have a foul odor in the exhaled breath. 2, atrophic rhinitis, paranasal sinusitis, nasal tumors or foreign bodies in the nasal cavity, due to local inflammation, increased secretions, more pus necrotic tissue and a large number of bacteria, when breathing through the nose, the nasal cavity will emit unpleasant nasal gas. 3. Patients with lung abscess and bronchial dilatation combined with infection, in addition to spitting out a large amount of pus-smelling sputum, also have pus-smelling odor in the exhaled gas. Indigestion caused by over-eating or gastritis caused by unclean diet, food fermentation in the stomach, belching, can have a sour and rotten smell. 4, embedded in the teeth or dental caries in the food residue corruption and fermentation, there can be unpleasant halitosis. Second, the peculiar food odor 1, diabetic patients with ketoacidosis, can exhale apple-like sweet smell; 2, a variety of organophosphorus pesticide poisoning, can exhale the general special garlic-like odor; 3, accidentally taking rodenticide zinc phosphide or eating onions, garlic too much, the body, especially in the mouth can also be issued the same smell; 4, typhoid patients can smell the smell of toast; 5, lymphatic tuberculosis patients have a kind of beer smell; 6, cyanide poisoning, the mouth has the smell of beer. 6, cyanide poisoning, there is an almond smell in the mouth; 7, tannery workers in the occurrence of hydrogen sulfide poisoning, can exhale rotten egg-like odor. Third, the strange animal odor 1, liver function is severely impaired liver coma patients, exhaled gas often emits a special rat odor, called liver odor; 2, yellow fever patients with pork odor; 3, odd sweating patients often emit fox odor; 4, measles children can emit chicken feather smell. 4, special excretion odor 1, uremic patients, due to impaired renal function, can not excrete waste normally, can cause the retention of nitrogen and other metabolites, creatinine, urea in the blood is significantly higher, the patient exhaled gas has a fecal odor; 2, gum bleeding, upper gastrointestinal bleeding or bronchial dilatation hemoptysis patients, there is often a blood odor in the mouth. Loss of smell 1. When tumor grows in the brain, due to the compression of olfactory center and nerve, the olfactory information cannot be transmitted in or out normally, which may lead to olfactory impairment; 2. Physiological olfactory cells and olfactory nerve aging, the sense of smell will also gradually diminish. Therefore, after middle age, if abnormal odor appears in the oral cavity or if the sense of smell gradually decreases or is lost for no obvious reason, it should be taken seriously.