Belching with the odor of rotten eggs refers to the bad breath that emanates from the mouth that annoys others and embarrasses oneself. Don’t underestimate the small problem of bad breath, it will make people (especially young people) dare not interact with people in close proximity, thus creating an inferiority complex, affecting normal interpersonal, emotional exchanges, people are very distressed. Belching with the odor of rotten eggs differential diagnosis: fishy odor: foul breath in the mouth, more than stomach heat prevalence. Periodontal inflammation, oral erosion, dental caries caries hole in the food debris embedded in the corruption and fermentation, can emit a fishy odor. Atrophic rhinitis, paranasal sinusitis, nasal tumors, due to local inflammation, increased secretions, with more pus and necrotic tissue and a large number of bacteria, breathing through the nose, the nasal cavity can emit unpleasant odor. Elderly people with bronchial dilatation have a large amount of pus and sputum, and the exhaled breath has a fishy odor. Gastritis caused by indigestion or unclean diet due to overfeeding, where food ferments in the stomach and belching has a sour and putrid odor. Rotten apple odor: This is an odor of ketone bodies. Under normal circumstances, the ketone bodies formed by the human body can be oxidized by the tissues at any time, the elderly diabetic patients due to a variety of reasons such as acute infection, pancreatic inflammation, trauma, major surgery, anesthesia, interruption of insulin therapy or insufficient dosage and the patient’s resistance to insulin, etc., which can make the body relative or absolute lack of insulin, sugar utilization is reduced, the decomposition of fats and proteins accelerated to produce a large number of ketone bodies, and it is too late to oxidize and excrete out of the body. The ketone bodies are produced in large quantities and are too late to be oxidized and excreted. In this way, the concentration of ketone bodies in the blood increases significantly, ketoacidosis occurs, and when the elderly breathe, there is a rotten apple odor. Ammonia or urine odor: the presence of severe uremia in the elderly, due to severe renal impairment, can not normally excrete waste, can cause nitrogen and other metabolites retention, blood creatinine, urea nitrogen increased significantly, the patient’s breath has a special ammonia flavor or urine odor. Rat odor: When liver function is seriously impaired and hepatic coma occurs in the elderly, a special rat odor is often emitted in the breath, which is called liver odor in medicine.