Baby Formula Side Effects Facts
Common Side Effects
Digestive problems, cow’s milk or soy protein allergy
Serious Side Effects
Cronobacter infection, severe cow’s milk allergic reactions, necrotizing enterocolitis (NEC)
Warnings and Precautions
Prepare formula in a sterilized environment and store it properly to avoid potential bacterial contamination.

Common Baby Formula Side Effects

Common baby formula side effects such as rash and digestive issues are most often caused by food allergies, contaminated formula or consuming improperly made formula.

For example, many manufacturers use cow’s milk as an ingredient in baby formulas, yet cow’s milk allergy is a common childhood allergy. About seven percent of babies younger than 12 months of age are allergic to the protein in cow’s milk.

Incorrectly made formula can also harm your baby. The CDC warns parents not to use homemade infant formula or buy imported formula online from third-party sellers because of potential problems like insufficient nutrition, dangerous electrolyte imbalances or contamination.

All baby formula legally sold in the US follows the FDA’s guidelines for safety and nutrition. For example, in August 2021, the FDA announced a baby formula recall for formulas made by Able Groupe because the formulas didn’t contain enough iron. Iron-deficiency anemia in infants could lead to irreversible cognitive and functional development problems.

Serious Baby Formula Side Effects

Baby formulas rarely cause serious side effects. However, if left unchecked, food allergies, nutrient deficiency or baby formula contamination can lead to serious health problems.

Infographic of serious but rare baby formula side effects.

Premature babies may also develop a serious condition called necrotizing enterocolitis (NEC) when drinking cow’s milk baby formulas such as Enfamil or Similac. About one in 1,000 infants who were born prematurely are affected by NEC. The risk is highest in babies who weigh less than two pounds at birth.

Food allergy symptoms such as swelling of the mouth or throat, hives and vomiting are a medical emergency. These are rare and can happen within days to weeks of an infant starting cow’s milk baby formula. Infants may also have an allergy to soy protein formula. If your infant exhibits any of these symptoms, consider seeking emergency medical attention immediately.

Baby formula has all the nutrition needed by a baby, but studies show formula-fed babies may have a greater risk of obesity, respiratory infections, sudden infant death syndrome (SIDS), cognitive development issues, allergies and other health risks compared to breastfed babies.

Rarely, a type of bacteria called Cronobacter may contaminate baby formula. This can happen during manufacturing, home preparation or during feeding from unsanitary bottles.

In February 2022, Abbott issued a baby formula recall for certain lots of its Similac, Alimentum and EleCare formulas after three complaints of Cronobacter infection and one complaint of Salmonella infection in infants who consumed the formula. Later that month, Abbott expanded the recall after the reported death of at least one infant infected with Cronobacter. In March 2022, FDA inspectors observed several zones that tested positive for the presence of Cronobacter in the Abbott factory that manufactured the affected formulas.

Babies younger than three months or with weakened immune systems are especially susceptible to bacterial infections. Be sure to prepare infant formula in a clean, sanitized area and keep your hands clean.

What Is Necrotizing Enterocolitis (NEC)?

Necrotizing enterocolitis is a gastrointestinal disease that usually affects infants. It’s fatal in up to 50% of all cases, according to a 2022 study published by the National Center for Biotechnology Information. NEC causes inflammation that can cause tissues in the intestine and colon to die. It may lead to holes in the intestine, sepsis and death.

Senior Writer Michelle Llamas discusses what necrotizing enterocolitis is and how it has been linked to baby formula.

NEC symptoms include lack of appetite, tenderness or swelling in the abdomen, bloody stools, vomiting and sluggishness. It typically affects babies between three and 12 days after birth but can occur many weeks after.

Studies show that premature babies who consume cow’s milk formula alone or as a supplement to breastfeeding are more likely to develop NEC. One of the first studies to link cow’s milk formula to NEC was a 1990 study published in the Journal of Medical Science which showed that NEC was up to 10 times more common in formula-fed premature babies.

Baby formula lawsuits are being filed against the makers of Enfamil and Similac by the parents and guardians of premature babies who developed NEC.

Lawsuit Information
Lawsuits are being filed by parents whose children were diagnosed with necrotizing enterocolitis (NEC) after consuming cow's milk-based formula.
Learn more

Side Effects of Changing Baby Formulas

Signs that a baby isn’t tolerating a formula well include diarrhea, constipation, gassiness or frequent vomiting. More serious intolerance issues include bloody stools, congestion or wheezing after eating.

Not all babies experience side effects from switching baby formulas, but when they do, the effects are usually mild digestive issues.

Sometimes your baby’s pediatrician may recommend changing your baby formula. It may be because of food allergies, formula intolerance or other medical concerns. However, changing a baby’s formula too quickly can be a shock to their sensitive digestive system.

Parents should transition a baby to a new formula by slowly adding it to feeding times. Consider consulting your pediatrician on how to transition your baby to a new formula safely and on how long to test a new formula to avoid side effects.

Editor Lindsay Donaldson contributed to this article.

Please seek the advice of a medical professional before making health care decisions.