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Causes of Allergic Colitis in Infants

By Maria Hoven ; Updated June 13, 2017

Allergic colitis is caused by an immune reaction to the proteins in your infant's diet. Most common proteins that trigger the condition are those found in cow, soy and breast milk, according to Children's Hospital Boston. Allergic colitis occurs primarily in infants and can result in blood in the stool, vomiting, diarrhea and a reduction in appetite. If you suspect your child may have allergic colitis, seek medical attention immediately.

Immune System

Allergic colitis usually develops during the first two months of life and affects 66 percent of infants. Your baby is more susceptible to allergic colitis due to her immature immune system. Normally, your immune system reacts only to harmful, disease-causing microbes. However, if your baby suffers from allergic colitis, her immune system mistakes the milk proteins as harmful and attacks them.

Protein Intake

Your baby is also at risk due to the high intake of milk and milk proteins from breast milk or formula. Because infants have immature immune systems, those with allergic colitis can react to the proteins in foreign substances to which they are suddenly exposed to after birth. If your infant with colitis continues to consume milk proteins, her intestines may gradually become irritated and inflamed, leading to tiny ulcerations in the colon and bleeding. If you or your baby's other family members have a history of food allergies, asthma or environmental allergies, your baby may be more susceptible to colitis, according to the Children's Hospital Boston.

Intestinal Permeability

Infants may also have increased intestinal permeability often associated with an immature digestive system, malnutrition and intestinal inflammatory diseases. If your baby suffers from this condition, her intestines are so permeable that even whole proteins can enter the bloodstream and trigger allergic colitis. Normally, your digestive system breaks down the proteins to amino acids or smaller peptide chains, which are then absorbed by your body. These are less likely to trigger a reaction than intact proteins.


After your infant has been diagnosed with allergic colitis, treatment begins by removing all sources of food that can cause the allergy from your baby’s diet. Your pediatrician usually recommends that you replace your current formula with a specialized, hypoallergenic or protein hydrolysate formula that contains broken-down proteins to help ease the stress on your infant’s digestive system. If neither if these formulas works, your infant may need an amino acid-based formula. If you are breast-feeding, your baby may show improvement when you remove cow's milk, eggs, soy, fish and wheat from your diet. This may allow your infant to continue to breast-feed as long she is gaining weight and thriving.


Allergic colitis is rarely life-threatening, unlike true milk allergy, according to the Children's Hospital Boston. Allergic colitis is usually a temporary condition, and most infants outgrow it by 1 year of age. You should begin introducing solids to your baby's diet as with any other infant -- when she reaches 4 to 6 months of age. However, pay attention to the food labels and avoid all products that contain milk, soy or their proteins.

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