Necrotizing Enterocolitis (NEC)

Necrotizing enterocolitis (NEC) is a rare but serious intestinal disease that’s most common in premature infants, especially those fed baby formula. NEC causes inflammation that leads to bacterial infections and intestinal tissue damage that could be fatal.

Last Modified: March 28, 2024
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What Is Necrotizing Enterocolitis?

Necrotizing enterocolitis, commonly known as NEC, is a rare, serious condition that affects the intestinal health of newborn babies. NEC causes tissue in the small or large intestine to become inflamed.

NEC usually happens in premature babies born before 37 weeks.

The inflammation kills tissue in the baby’s intestinal tract and allows bacteria to infect the colon. These infections are serious and can be fatal.

NEC can affect any infant, but most newborns who get the disease are born prematurely or are sick. In fact, it’s the most common gastrointestinal condition in premature babies. It’s also more common in premature babies that have been fed preemie formula than those who have been fed breast milk.

Types of NEC

There are four main types of NEC classified by what causes the condition and when symptoms start. The most common type, called classic NEC, affects premature babies.

Four types of NEC are:
Some newborns get NEC in the first week of life, but this is rare.
Affects babies born before 28 weeks and can occur as early as three weeks after birth. This is the most common type of NEC, and symptoms start suddenly and can affect babies who are stable.
Term infant:
Babies with birth defects born full term
About 33% of preemies can develop NEC within three days of receiving blood transfusions for anemia.

In the 1970s, medical providers introduced the first NEC Bell staging system based on severity of symptoms. Providers have since modified the staging system. Stages go from IA (suspected NEC with lethargy) to IIIB (advanced NEC with perforated bowel).

What Causes NEC?

Researchers don’t know the exact cause of NEC, but the two most common factors in babies with NEC are premature birth and formula feeding.

Scientists think premature babies are more susceptible to NEC because their lungs and intestines are not fully developed. Oxygen-carrying blood has a harder time reaching the intestinal lining and this could lead to tissue damage.

Who’s at Risk?

Premature babies fed baby formula have the greatest risk of developing NEC, but babies who have other illnesses or those who are born with birth defects can also get NEC.

Babies are most likely to get NEC while still in the hospital.

Risk factors for NEC include:
  • Formula feeding, especially cow’s milk baby formula
  • Intestinal infections
  • Low birth weight of under 5.5 pounds with the greatest risk for babies under 2 pounds
  • Low oxygen level at birth
  • NICU or nursery bacterial outbreaks
  • Premature birth (born before the 37th week of pregnancy)
  • Serious illness
  • Transfusions
  • Feeding with a tube inserted into the stomach, also called enteral feeding

Studies have shown that babies fed human milk have a lower risk of NEC. Scientists think human milk may contain growth factors, antibodies and immune cells that may be protective for babies, but more research is needed.

How Common Is NEC?

NEC is a potentially fatal condition, but fortunately it’s not very common in the general population of infants.

It affects about one in 10,000 full-term babies and one in 1,000 premature babies. According to experts, it’s the most common gastrointestinal emergency for premature infants in the neonatal intensive care unit.

NEC and Baby Formula

Since the 1990s, researchers have published studies on the topic of breastfeeding and formula that suggest premature infants exclusively fed baby formula have a greater risk of NEC compared to babies fed human breast milk or a mix of breast milk and formula.

The link between NEC and baby formula has spurred some parents to file baby formula lawsuits against Abbott Laboratories and Mead Johnson, the makers of popular formula brands Similac and Enfamil. According to lawsuits, Abbott and Mead Johnson knew their products could increase the risk of NEC but failed to warn the public of the potential for baby formula side effects in premature infants.

In February 2022, Abbott issued a baby formula recall for lots of Similac manufactured in its Michigan factory because some babies who used the formula got bacterial infections.

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

What Are the Symptoms of NEC?

Symptoms of NEC range from mild, early symptoms such as lethargy to more serious symptoms such as bloody stool and green or yellow vomit.

Symptoms of NEC include:
  • Inability or refusal to feed
  • Distended, swollen abdomen
  • Blood in the stool
  • Yellow or green vomit
  • Lethargy
  • Inability to gain weight
  • Abdominal pain
  • Changes in blood pressure, breathing and heart rate

The most serious symptoms that may indicate advanced disease or bowel perforation include fluid buildup in the abdomen, pain and metabolic acidosis — a buildup of acid because of kidney problems. Babies who develop NEC may also suffer from complications such as developmental problems and death before hospital discharge.

What Are Possible Complications of NEC?

NEC is a serious disease with potentially grave complications, especially if the infection isn’t detected early. The baby may develop breathing problems, slow heart rate and narrowed intestines. In the most serious cases, holes develop in the inflamed bowel walls and bacteria leaks out of the gut and into the blood, causing sepsis.

The lack of nutrients and oxygenated blood flow can lead to neurodevelopmental problems and poor growth rate. If NEC is severe enough to damage the intestine, the baby may develop short gut syndrome. Children with short gut syndrome will need care for the rest of their lives to get the right nutrition to grow and stay well. This may require tube feeding.

Having NEC increases the chances of death in premature babies. Studies show the mortality rate of infants with NEC is 20% to 45%, although some place it as high as over 50%.

Fortunately, data shows that mortality rates of infants with NEC may have decreased over the years, even as case numbers remained stable. Cleveland Clinic suggests eight in 10 babies with NEC survive, but some may have long-term health problems such as chronic digestive issues.

How Is NEC Diagnosed?

NEC is typically diagnosed with a physical examination and radiological tests after symptoms of digestive issues or infection emerge. Medical providers can confirm an NEC diagnosis with an X-ray that shows abnormal gas patterns in the intestinal walls.

The X-ray may show gas outside the abdomen, thickened bowel walls and fluid buildup. Doctors will also do blood tests for blood gases, acidosis, anemia and how well the blood clots. Free air inside the abdominal cavity, called pneumoperitoneum, is an indication of a bowel perforation and is a surgical emergency.

Treatments for NEC

Treatment for NEC starts immediately after diagnosis to prevent more serious complications. The first thing doctors will do is to stop all feedings. From there, medical providers will insert an IV to deliver fluids and nutrition.

The baby will then receive antibiotics to prevent or treat infection. Doctors will constantly monitor the baby with X-rays and exams to assess the progression of disease. If the baby’s condition worsens, doctors may have to perform surgery to check for holes in the bowel and remove any dead intestinal tissue. If the damage is minor, the surgeon will sew the intestine back together.

Sometimes a large section of the bowel may be removed and the doctor will bring part of the intestine to the side of the abdomen so the stool can safely exit the body through an abdominal opening and into a bag. This is called an ostomy. In about six to eight weeks, the doctor will repair the hole when the intestine is healed.

Your baby can go home when they are eating and not losing weight. You may wish to ask your doctor for additional health information, including details on clinical trials or investigational treatments, if your baby isn’t responding to traditional NEC treatment. You can also check online at

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