Baby diarrhea sour smell partly belongs to physiological, partly caused by indigestion or lactose intolerance and other reasons. 1. physiological factors: breast milk and milk powder are high protein diet, protein and fat in the intestinal fermentation, the baby defecation and exhaust will have a sour smell, observe the stool for paste yellow dilute stool accompanied by a small amount of milk petals. The baby ate milk well, no other discomfort, usually considered physiological factors, generally does not affect the baby’s growth and development. 2. indigestion: baby stool thin, sour odor partly because of indigestion, most and irregular feeding, cold and other bad factors. The performance of the stool increased, more milk petals, some with bloating, vomiting, loss of appetite and other discomforts. 3. Lactose intolerance: mostly seen in babies who eat breast milk, part of the breast milk lactose content is high, the baby intestinal lactase enzyme is insufficient or decreased activity, can not be well digested lactose and lead to abnormal fermentation in the intestinal tract, which manifests the thinning of the stools more often, acidic and heavy odor, and a lot of foam or mucus blood, and so on. In addition, there are also enteritis can also cause diarrhea sour smell, stool frequency or accompanied by other discomforts, etc. It is recommended to interview the doctor and stool tests to further clarify the cause of the disease, to avoid affecting the growth and development of the baby.