There are several reasons why the stool is smelly: 1, eat a lot of high protein, high nutritional value of food, the gastrointestinal can not be well digested, absorbed, food in the gastrointestinal decomposition by bacteria, fermentation, it will produce a lot of odor very smelly indole, resulting in very smelly stool. 2, intestinal aging, usually occurs in the middle-aged and elderly, but also some young people do not pay attention to dietary health, long-term use of intestinal irritation is very strong 3, dry stool, if there is constipation, stool in the intestinal tract for a long time, under the action of intestinal bacteria, the stool will gradually ferment and become very smelly. 4, intestinal diseases, such as enteritis, intestinal cancer, etc. will lead to abnormal intestinal function, intestinal peristalsis becomes slower, intestinal flora dysbiosis, may also lead to very smelly stool. 5, the Lactose intolerance, if the body lacks lactase, a lot of lactose will accumulate in the intestine, under the action of bacteria lactose will decompose, fermentation and produce very smelly gas, resulting in very smelly stool.