If you either want to or need to use a breast milk substitute such as formula for your infant, it is best to start with one of the cow milk formulas that are fortified with iron. Most infant formula is made with cow’s milk that has been altered to resemble breast milk. This alteration gives the formula more appropriate amounts of carbohydrates, protein, and fat for human infants. Most babies thrive on cow’s milk formula, but some babies fare better with other types of infant formula, either soy or protein hydrolysate. Soy-based formula is an alternative for babies who are allergic to the proteins in cow’s milk formula or who can’t tolerate lactose, a sugar naturally present in cow’s milk. Protein hydrolysate formula is meant only for babies who have a family history of milk allergies since it is easier to digest and less likely to cause allergic reactions than the other types of formula. No matter which specific formula you choose, all infant formulas come in three preparations: powdered which is the least expensive, concentrated liquid, and ready-to-use which is the most expensive.