Three-month infant diarrhea sour smell can belong to the normal physiological diarrhea, can also be seen in the dietary factors or infection caused. 1. Physiological diarrhea: most common in infants less than 6 months, breastfeeding is the main, in addition to the increased frequency of stools, no other symptoms, good appetite, does not affect growth and development. 2. Dietary factors: due to overfeeding or improper composition of the mother’s diet can cause diarrhea in infants. 3. Infection: when there is a mild intestinal infection, it can cause loss of appetite, increased frequency of stools, diarrhea and sour smell. Three-month-old babies with sour odor, there may be other reasons, it is recommended to go to the hospital in time to improve the examination to clarify the cause of the disease, under the guidance of the doctor to give targeted treatment or treatment.