Soy formula is not the formula of choice for babies with milk protein allergy. Studies looking at this problem have shown that up to 50% of infants who react to cow’s milk protein will also react to soy protein. So if your baby has true signs of milk protein allergy, you’re playing the odds by switching to soy. A casein hydrolysate formula such as Nutramigen or Alimentum are considered the first line formulas of choice for the milk allergic baby.