4 months old baby stools sour, mainly due to indigestion, lactose intolerance, according to the specific situation, the cause of treatment. Common causes and treatments 1, indigestion: 4 months baby digestive system function is not well developed, digestive enzyme secretion is not enough, parents feed too much will be easy to appear indigestion symptoms, manifested as sour stools, can be under the advice of doctors, the use of probiotics such as bifidobacteria, Saccharomyces boulardii regulate intestinal flora to improve digestive function, while appropriate clockwise massage abdomen, promote intestinal peristalsis, to improve the symptoms. Symptoms. 2. Lactose intolerance: Because the lactose content in breast milk or milk powder is high, and the gastrointestinal tract function of infants is not yet well developed, resulting in lactose not being fully digested and absorbed. When the undigested lactose will gradually ferment in the intestines, resulting in sour smelling stools, and can be accompanied by diarrhea symptoms. When this phenomenon occurs in babies, mothers need to add lactase drops to breast milk or formula under the guidance of a medical professional. To help break down and absorb lactose. If the diarrhea is severe, breastfeeding should be stopped and lactose-free formula should be fed according to medical advice. The mother should follow a small number of meals in feeding, do not feed too much at a time, and also apply hot compresses to the baby’s abdomen, but pay attention to keep the abdomen warm and avoid getting cold.