Sour odor in baby’s stool may be related to physiological factors, or it may be caused by indigestion, lactose intolerance, intestinal inflammation and other reasons. 1. Physiological factors: Breastfed babies often have a slight sour taste in their stools, which is a normal physiological phenomenon, and babies usually do not show any other signs of discomfort, so no special intervention is needed. 2. Indigestion: As the gastrointestinal system of infants is still immature, the digestive function of the gastrointestinal tract is relatively poor, if there is improper feeding, it is likely to lead to indigestion, which may result in the baby’s stools having a sour taste, and may be accompanied by abdominal distension, abdominal pain and other manifestations. 3. Lactose intolerance: it is usually due to the lack of lactase enzyme or insufficient secretion in the body of infants, resulting in the inability to fully digest and absorb the lactose in food, which may cause the stool to have a sour taste, and may be accompanied by abdominal distension, diarrhea and other manifestations. 4. Intestinal inflammation: Due to bacterial and viral infections in the intestines, there are more pathogenic bacteria in the intestines, which may cause the baby’s stools to have a sour smell, and may be accompanied by vomiting, diarrhea and other manifestations. The acidic odor of the baby’s stool may also be caused by other reasons. After eliminating physiological factors, it is recommended to consult a doctor as soon as possible to clarify the cause and then give targeted treatment and adjustment.