If the baby eating formula baby poop sour smell is normal, usually due to the following reasons: because the baby is young, the digestive system is not fully developed, after eating some food easily caused by stomach discomfort, thus causing indigestion, baby poop is sour smell. If the odor is very obvious, it may be due to protein indigestion, it is recommended to reduce the amount of milk powder or to dilute the milk powder. If your baby eats too much every day, it can also cause foul-smelling stools. If your baby’s stool smells sour because of incomplete digestion of carbohydrates in the baby’s body, it is recommended that you supplement your baby with nutritional probiotics while feeding him/her formula, because probiotics are good for the baby’s digestion of formula and can relieve the symptoms of sour stool. If the baby is breastfed, it is normal to have a sour smell, but not a foul smell. The mother’s daily diet is also related to the secretion of milk, which also plays a role in the baby’s digestion. It is not advisable to consume too much protein and fat in the daily diet, and it is recommended to eat a light diet and relax. Usually the sour smell of the baby’s poop is caused by the incomplete digestion of proteins and carbohydrates in the body’s digestive system.