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Baby Formula Side Effects

Formula-fed babies are more likely to have respiratory infections and food allergies than breastfed babies. Common baby formula side effects include eczema, upset stomach and runny nose. In rare cases, formula may cause necrotizing enterocolitis, or NEC, in premature babies.

Last Modified: September 5, 2023
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Common Baby Formula Side Effects

Common baby formula side effects are typically caused by food allergies, contaminated formula or using a formula that was made improperly.

For example, many baby formulas are made with cow’s milk, and cow’s milk allergy is one of the most common childhood allergies. About seven percent of babies younger than 12 months of age are allergic to the protein in cow’s milk, according to the UK’s National Health Service.

Symptoms of cow’s milk allergy include: Skin reactions, stomach problems, stuffy nose and eczema. Severe allergies may cause swelling and difficulty breathing.

Feeding baby formula made incorrectly 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 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. But food allergies, nutrient deficiency or baby formula contamination can lead to serious health problems if left unchecked.

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

Life-threatening 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 after starting cow’s milk baby formula. Babies may also be allergic to soy protein formula. Seek emergency medical attention right away.

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

Rarely, baby formula may be contaminated with a type of bacteria called Cronobacter. This can happen during manufacturing, home preparation or during feeding if bottles aren’t properly cleaned.

In February 2022, Abbott issued a baby formula recall for certain lots of its Similac, Alimentum and EleCare formulas after a few babies got sick from Cronobacter infections and some died. In March 2022, FDA inspectors observed several places that were 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, and Cronobacter can cause serious and potentially fatal infections. Make sure to prepare infant formula in a clean, sanitized area and keep your hands clean.

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

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 article. 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.

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 fed 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 that showed that NEC was up to 10 times more common in formula-fed premature babies.

Parents of premature babies that developed NEC are filing baby formula lawsuits against the makers of Enfamil and Similac for failing to warn them of the risk.

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.
View Lawsuits

Side Effects of Changing Baby Formulas

Sometimes, your baby’s pediatrician may recommend changing baby formulas. It may be because of food allergies, formula intolerance or other medical concerns. Some babies may have side effects from switching baby formulas, but they are usually mild digestive issues, such as changes in stool.

Signs a baby isn’t tolerating a type of formula well include: Diarrhea, constipation, gassiness or frequent throwing up. More serious intolerance issues include: Bloody stools, congestion or wheezing after eating.

It can be a shock to a baby’s sensitive digestive system if you change formulas too quickly. Parents should transition a baby to the new formula by slowly adding it into feeding times. Make sure to consult your pediatrician on how to properly transition your baby and how long to test a new formula to avoid side effects.

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