New mothers are advised that breastfeeding is best for their newborn, but in some cases, it is not possible or practical. For these babies, nutrition will be supplied through infant formula. Today, many types of formulas are on the market. The U.S. Food and Drug Administration regulates infant formulas in the United States to ensure they meet specific nutritional guidelines. Formulas not meeting these standards are considered "adulterated," although some formulas, including those designed for premature babies or those with certain medical conditions, are exempt from these standards. Consult with your pediatrician before deciding which formula is best for your baby.

Milk-Based Formula

Milk-based infant formulas are by far the most commonly purchased products, accounting for about 80 percent of U.S. formula sales, according to the American Academy of Pediatrics. These formulas are made from cow's milk, but they are processed in such a way to make it easier for babies to digest and safe for them to eat. In addition, milk sugar, or lactose, is added and some butter fat is replaced with vegetable-based oils to make it more similar to breast milk and suitable for promoting growth and development. Most healthy babies who do not have food allergies can safely drink milk-based formulas.

Soy Formula

Soy-based formulas use soy as the protein source and also contain an added carbohydrate to meet the baby's nutritional needs, according to the American Academy of Pediatrics. These formulas are often recommended for babies who are lactose-intolerant or who are allergic to milk. However, many babies with milk allergies are also allergic to soy, so you may not see a noticeable improvement after switching. The American Academy of Pediatrics does not typically recommend soy-based formulas unless a baby has a rare medical condition called galactosemia, which makes them unable to drink any formula containing lactose. Some vegetarian families also opt for soy formulas because they contain no animal products.

Lactose-Intolerant Formula

Lactose-free formulas are another type of milk-based formula, but they have been altered for babies who cannot tolerate the milk sugar lactose. In these formulas, the lactose is removed and replaced with another carbohydrate source, such as corn syrup, according to BabyCenter.

Hydrolyzed Formulas

Hydrolyzed formulas are another type of milk-based formula, but in these products, the protein has been partially broken down into smaller protein units. These formulas, which are sometimes referred to as hypoallergenic or predigested formulas, are often recommended for babies who have or are prone to food allergies or those who cannot be exclusively breastfed for at least four months, according to the American Academy of Pediatrics. Although more expensive than other formulas, they are effective: at least 90 percent of babies with food allergies benefit from using a hydrolyzed formula.

Premature Baby Formulas

Babies who are born prematurely or have a low birth weight are often given a special formula designed to meet their nutritional needs. These babies often need to consume more protein and calories than babies who are born full-term, so special formulas have been produced to meet these needs, according to BabyCenter.

Metabolic Formulas

Babies with certain medical conditions, including metabolic disorders, need to use specialized formulas specifically designed to meet their nutritional needs. These formulas, called metabolic formulas, vary depending on your baby's medical condition. Some of these formulas are available by prescription and may be covered by your health insurance.