Recently, the old exhaust odor has the following reasons: 1, intestinal flora imbalance, resulting in an increase in harmful bacteria in the intestine, the intestines in the process of digesting food, the bacteria in the intestines will produce a lot of sulfur compounds, such as hydrogen sulfide, which will lead to the discharge of gas with a foul odor, resulting in the old exhaust odor. 2, constipation, constipation, the stool will be retained in the intestinal tract for a long time, the stool bacteria will produce a lot of odor, so it will lead to the old exhaust odor. 3, eat too much legumes, because legumes contain a lot of cotton candy, which is a kind of oligosaccharide, but there is no enzyme in the intestine that can digest this oligosaccharide. 3, eat too much soy food, because soy food contains a lot of cotton candy, is a kind of oligosaccharide, but there is no enzyme in the stomach and intestines can be digested this oligosaccharide, so it will lead to the old exhaust odor, and sometimes lead to bloating. 4, lactose intolerance, part of the body lacks the enzyme that can digest lactose, which leads to lactose is not digested from the small intestine to the colon, the lactose will be broken down by the bacteria in the colon, resulting in a lot of very smelly gas, leading to the old exhaust odor. Lactose is broken down by bacteria in the colon, resulting in the production of a lot of very smelly gas, leading to the old exhaust odor.