Four-month-old baby poop sour odor may be lactose intolerance, dyspepsia, enteritis and other diseases caused. 1. Lactose intolerance: Lactose intolerance is mainly caused by congenital lactase gene deficiency or damage to the intestinal mucosa by various factors such as acquired infections and medications. Children with lactose intolerance may suffer from abdominal distension, hyperactive bowel sounds, diarrhea, etc. Diarrhea is mainly yellow loose stools with foam and sour smell, and nausea, vomiting and other symptoms. 2. Dyspepsia: The onset of dyspepsia is affected by a variety of factors, such as gastrointestinal dyskinesia, decreased gastric tolerance, heredity and so on. The main symptoms are postprandial fullness, abdominal pain, diarrhea, constipation, etc., which can also lead to the phenomenon of sour stool. 3. Enteritis: enteritis is mainly due to bacterial, viral and other pathogenic infections, immunity, radiation and other factors, the child will have abdominal pain, diarrhea, bloody stools, nausea, vomiting and other symptoms, which will also lead to the appearance of the child’s poop sour smell. Four-month-old babies with sour stool odor, there may also be other reasons, it is recommended to go to the hospital in a timely manner, improve the examination to determine the cause of the disease, under the guidance of the doctor to give targeted treatment or treatment.