NEC, or necrotizing enterocolitis, is a serious intestinal disease that primarily strikes premature babies, and its connection to cow’s milk-based formula has become a major concern for parents and the subject of hundreds of lawsuits. The disease causes inflammation and bacterial invasion of the intestinal wall, which can progress to tissue death and even perforation of the bowel. It carries a mortality rate as high as 50% and almost exclusively affects newborns, particularly those born very early or at very low birth weight.
The link between formula and NEC is nuanced. Human breast milk appears to protect premature infants from developing the disease, while cow’s milk-based formula does not offer that same protection. Whether formula actively causes NEC or whether the absence of breast milk removes a critical safeguard is still debated, but the practical takeaway is the same: premature infants fed formula face a meaningfully higher risk.
How NEC Damages the Intestine
In a healthy newborn, the intestinal lining acts as a barrier that keeps bacteria where they belong. In NEC, that barrier breaks down. Bacteria invade the intestinal wall, triggering severe inflammation that destroys cells and cuts off blood supply to sections of the bowel. As the disease progresses, affected tissue dies. In the most severe cases, the intestinal wall develops holes, allowing bacteria and stool to leak into the abdominal cavity, which can cause life-threatening infection.
This cascade can unfold over several days or appear suddenly. The disease most commonly affects the colon and lower portion of the small intestine, though it can involve any section of the bowel.
The Formula Connection
The products at the center of this issue are not the standard formula you find on store shelves. They are specialized cow’s milk-based formulas and human milk fortifiers designed for use in hospital neonatal intensive care units. These products, including versions of Similac and Enfamil, are formulated specifically for premature and very low birth weight infants who need extra calories and nutrients to grow.
A meta-analysis comparing formula-fed preterm infants to those receiving donor breast milk found that formula was associated with an 87% higher risk of NEC. Another systematic review found the comparison even starker: infants fed donor human milk were three to four times less likely to develop NEC than those fed formula. A joint report from U.S. regulatory agencies and a National Institutes of Health working group concluded in 2024 that current evidence supports the idea that it is the absence of breast milk, rather than exposure to formula itself, that drives the increased NEC risk. That distinction matters scientifically, but for parents of premature babies, the implication is the same: breast milk offers protection that formula does not.
Symptoms Parents Should Recognize
NEC symptoms can appear gradually or come on fast. The National Institute of Child Health and Human Development lists these common warning signs:
- Feeding intolerance: the baby cannot digest food properly
- Abdominal swelling or bloating
- Stomach discoloration: the skin over the belly turns bluish or reddish
- Pain when the abdomen is touched
- Bloody stool or changes in stool color and consistency
- Vomiting greenish-yellow liquid
- Lethargy: noticeably decreased activity
- Episodes of slowed heart rate or pauses in breathing
- Inability to maintain normal body temperature
In a NICU setting, nurses and doctors monitor for these signs closely. Parents who notice any of these changes should alert the care team immediately.
How NEC Is Diagnosed and Staged
Doctors use a system called Modified Bell’s Staging to classify NEC severity. At Stage I, the disease is only suspected. The baby shows nonspecific symptoms like feeding intolerance, and imaging looks normal or shows mild intestinal sluggishness. Many babies at this stage turn out not to have NEC at all.
At Stage II, the diagnosis is confirmed. X-rays reveal a hallmark finding: small bubbles of gas trapped within the intestinal wall, a sign that bacteria have invaded the tissue. More severe Stage II cases show gas in the blood vessels leading to the liver. By Stage III, the baby is critically ill. Free air visible in the abdominal cavity on imaging means the intestine has perforated, and surgery is typically required.
What Happens After a NEC Diagnosis
Many infants with NEC require surgery to remove dead sections of bowel. That surgical reality creates a significant burden of long-term complications. In a survey of NEC survivors and their parents, 72% of parents and 89% of survivors reported lasting health effects. Among adult survivors in the study, 36% had been diagnosed with short bowel syndrome, a condition where so much intestine has been removed that the body struggles to absorb nutrients properly. Fourteen percent reported cognitive difficulties affecting learning and schoolwork.
Other long-term complications include digestive problems like chronic belly pain and constipation, difficulties with fine and gross motor skills, respiratory issues, and prolonged dependence on tube feeding or intravenous nutrition. Studies examining children at age seven who survived NEC found increased rates of functional impairment and ongoing bowel problems. The emotional toll is significant too. One survivor quoted in the research described feeling “depressed and lonely” from the lasting effects of NEC and short bowel syndrome.
How Breast Milk Protects Premature Infants
The American Academy of Pediatrics recommends human milk as the preferred feeding for very low birth weight infants. When a mother’s own milk is unavailable, donor breast milk should be used instead. Both options still require fortification for premature babies, since unfortified human milk alone does not contain enough protein and calories for optimal growth in the smallest infants. Fortification to about 24 calories per ounce is standard for most.
For babies born under about 2.2 pounds, fortification of both human milk and formula is recommended, continuing for at least 12 weeks after hospital discharge. The protein content of breast milk naturally declines over time, which means even exclusively breastfed preterm infants need supplementation to avoid nutritional gaps. When neither the mother’s milk nor donor milk is available, nutrient-enriched preterm formula is the alternative, though it does not carry the same protective benefits against NEC.
The Lawsuits Over NEC and Formula
Nearly 1,000 lawsuits have been filed against Abbott Laboratories (maker of Similac) and Mead Johnson (maker of Enfamil, a unit of Reckitt) alleging that these companies failed to warn that their cow’s milk-based products for preterm infants could cause NEC. More than 700 of these cases are centralized in an Illinois federal court, with others moving through state courts in Illinois, Missouri, and Pennsylvania.
Juries have already returned significant verdicts. In 2024, a jury ordered Mead Johnson to pay $60 million to the mother of a premature baby who died after being fed Enfamil. Months later, a St. Louis jury ordered Abbott to pay $495 million in another case. Both verdicts are under appeal. A trial involving four families began in early 2025 in Cook County, Chicago. Meanwhile, a federal judge overseeing the centralized cases has dismissed three of four cases selected for initial trials, and no federal case has yet reached a jury. The legal landscape is still evolving, with manufacturers contesting the scientific basis for causation.