Infant milks are a specific type of infant formula where the protein is derived from cows' milk. Cows' milk contains too much protein and so the protein is altered to make it suitable for babies.

Infant milks are suitable from birth and can be either 'whey-based' or 'casein-based'.

In whey-based milks the cows' milk protein is adjusted so that the casein to whey ratio is similar to breastmilk (40:60).In casein-based milks there is more casein than whey. The ratio of casein to whey remains the same as cows' milk (80:20). Whey-based milks may also have a lower mineral content (in particular sodium and potassium) which is important for newborn babies who have immature kidneys.

Whey-based milks, therefore, are the first choice of milk if a mother does not breast-feed, whereas casein-based milks are generally used if the baby appears not to be satisfied on a whey-based product. They can also be helpful in delaying the introduction of solids before the recommended age.