Most pediatricians recommend that parents wait until a baby is 1 year old before introducing cow's milk, according to BabyCenter. A primary reason to delay whole milk is that babies digest breast milk or formula much more easily.
Babies may also have allergies to cow's milk. Lactose intolerance can cause significant problems for an infant, including bloating, cramping and diarrhea, reports Parenting. Cow's milk doesn't have the amount of iron that is present in breast milk and formula. Babies could become iron deficient without enough iron intake. They also need an ample supply of fat, and cow's milk doesn't provide the healthiest types.