The ABCs of Formulas

Medically Reviewed by Louise Chang, MD on July 01, 2010
4 min read

Babies fuss, cry, spit up, and get gassy. When they have these symptoms frequently, it's up to their parents to figure out what's wrong. Often the first place parents will look for clues is the baby's diet.

In their quest to soothe a fussy baby, many parents try changing formulas, assuming that the symptoms are caused by a formula intolerance. Up to half of all formula-fed babies are switched to a new formula in the first six months of life. Yet research finds that only about 2% to 15% of babies actually have a formula intolerance.

So how do you know whether your fussy baby is really having formula problems? Here’s how to recognize the signs of formula intolerance, and when to consider switching formulas.

There are four basic formula types:

  • Cow's milk formula with cow’s milk as the protein source and lactose as the carbohydrate source and typically enriched with iron. Soy-based formula with soy as the protein source and corn as the carbohydrate source and typically enriched with iron.
  • Hydrolyzed formula (also called hypoallergenic formula) is made with proteins that have already been broken down so they are easier to digest. Corn or sucrose is the carbohydrate.
  • Specialized formulas for premature babies or babies with certain disorders or conditions.

For most healthy infants, experts say cow's milk formula is the best place to start. "It's well tolerated, it's the cheapest, and it contains the nutrients babies need," says Ari Brown, MD, FAAP, a pediatrician in Austin, Texas, and co-author of Baby 411 and Expecting 411.

Try to stick with the same formula for at least six to eight weeks, even if your baby is crying, gassy, or spitting up. These aren't necessarily signs of formula problems -- they're just normal baby behaviors.

"All of the gassy, poopy stuff has nothing to do with the formula and everything to do with being a newborn," Brown says. "They are born with an immature gut and they eat 24 hours a day. If we ate 24 hours a day, we'd be gassy too." Most of the gassiness and other stomach discomfort should go away on their own by the time a baby is four to six months old.

Most babies do just fine on cow's milk formula, but a small percentage of infants can't tolerate it because of lactose intolerance (an inability to break down the lactose sugar in milk) or an allergy to the proteins in milk.

Brown says it's very rare for babies to be born with lactose intolerance. Most of the time, lactose intolerance doesn't start until after a child's first birthday.

About 2% to 3% of babies have a milk protein allergy, in which the baby's immune system mistakenly sees the milk protein as a foreign invader and attacks it. Most babies eventually outgrow their milk allergy.

How can you tell whether your baby really has a milk allergy? Common symptoms include rash, wheezing, upset stomach, vomiting, and diarrhea. Although less common, Joanne Cox, MD, associate chief of General Pediatrics at Children's Hospital Boston adds that blood in the stool is a tell-tale sign.

Call your pediatrician if you notice blood in your baby's stools, or any of the other symptoms of a milk allergy:

An allergist can test your baby for a milk protein allergy.

If your baby has a true milk allergy, here's a rundown of the non-cow's milk formulas you can try:


Soy formula is an option for babies with lactose intolerance. However, some babies with milk allergy have the same reaction to soy formula as they do to cow's milk formula.

Some parents put their babies on soy formula because they think it's easier to digest. Yet there is lack of evidence that soy formulas are helpful for babies with milk protein allergy or colic, according to the American Academy of Pediatrics (AAP).

The AAP recommends that use of soy formula be limited to babies with the rare disorders galactosemia or congenital lactase deficiency, which prevents the body from breaking down sugars in cow’s milk.

Hydrolyzed or Hypoallergenic

These formulas are most helpful for the small number of babies who have a true milk protein allergy. Research finds that hydrolyzed formulas can help improve allergy symptoms, and they also help allergic babies gain weight better than regular formulas. Some babies at high risk for allergies may also benefit from this type of formula. Your pediatrician would be able to tell you whether your baby should be using hydrolyzed formula.

If you think your baby has a formula intolerance, don't just switch from one formula type to another in an attempt to find one that works. "I don't think you're necessarily doing your baby any favors, because they might have some diarrhea or gas from switching around all the time," Brown says.

Frequently switching formulas also makes it harder to know for sure which ingredients are causing your baby's distress. Before you change to a new formula, check with your pediatrician. Once you make the switch, give your baby at least a few weeks to get adjusted.

Once your baby is older, you can try changing back to cow's milk formula. Just make the transition gradually, adding about an ounce of the new formula at a time, Cox advises.