Milk protein allergy (MPA), also known as food protein induced allergic proctocolitis (FPIAP), is one of the most common gastrointestinal disorders in young children, affecting up to 17% of infants. It most commonly occurs in infants less than 1 year of age. Children with a history of eczema or those who have a family history of food allergies in a parent or sibling may be at higher risk of developing milk protein allergy.
What is milk protein allergy?
Infants with milk protein allergy develop inflammation in their intestines caused by an immune system response to one or more of the proteins found in food. In about 75% of cases, this is cow’s milk. However, sometimes other foods proteins can trigger this immune response, including egg, soy and corn. The intestinal inflammation that occurs in milk protein allergy can lead to a variety of symptoms, including discomfort, loose bowel movements or bloody stool. Treatment for milk protein allergy centers around removing the triggering food protein from the infant’s diet. In most cases, children outgrow a milk protein allergy by 1 year of age.
Milk protein allergy symptoms
Infants with MPA may present with a variety of symptoms, including:
Bloody stool
Mucous in the stool
Loose bowel movements
Fussiness or discomfort
Feeding problems
Slow weight gain
What causes a milk protein allergy?
MPA occurs when an infant’s immune system abnormally reacts to the complex proteins found in food. There are two different types of immune reactions that can occur to food proteins:
IgE-mediated (also known as immediate reactions): The immune system overreacts to an allergen by producing antibodies called immunoglobulin E (IgE). This causes symptoms of an immediate allergic reaction like hives, rash, wheezing and/or anaphylaxis.
Non IgE-mediated (also known as delayed reactions): The immune system abnormally reacts to a food protein through a pathway that does not involve IgE. This causes the delayed onset of gastrointestinal symptoms. The vast majority of MPA in infants is non IgE-mediated.
How is a milk protein allergy diagnosed?
MPA is diagnosed by a healthcare provider after taking a clinical history and performing a physical examination. In some cases, a food elimination and rechallenge can be helpful in making a diagnosis of milk protein allergy. There are no diagnostic tests that are sensitive or specific for milk protein allergy.
What's the difference between a milk allergy and a milk intolerance?
The terms “allergy” and “intolerance” can sometimes be confusing, as many people use the terms interchangeably. Both conditions can cause symptoms. However, the key difference is whether the immune system is activated or not. A food allergy occurs when the immune system reacts to a food. Babies with milk protein allergy have damage to their stomach and intestines because of the immune system response. In food intolerances, the immune system is not activated. Lactose intolerance is a common example of a food intolerance. People with lactose intolerance develop gastrointestinal symptoms because they have low levels of the lactase enzyme in their intestines, so they don’t digest the sugar lactose well. Lactose intolerance does not cause any damage to the intestines.
How to test for milk protein allergy in infants
A diagnosis of MPA is made based on clinical symptoms. No sensitive or specific diagnostic tests exist for milk protein allergy. In some cases, a child’s stool may be tested for the presence of microscopic blood. However, this test has high rates of false positive results, so it is not very accurate. Blood and skin allergy testing only detects IgE-mediated immediate reactions, and these tests are not helpful when evaluating delayed non-IgE-mediated reactions.
Treatment for milk protein allergy
As an attending physician at Boston Children's Hospital, I know that treatment for milk protein allergy involves removing the triggering food protein from an infant’s diet. It can take up to 2 weeks after making a dietary change to see improvement in symptoms.
For breastfed infants, the breastfeeding parent is usually asked to eliminate trigger foods from their diet, as proteins can be passed to an infant through breastmilk. In most cases, restriction of milk alone is sufficient. However, if a child does not improve with milk restriction, sometimes additional foods are restricted.
Formula-fed infants can be switched to a hypoallergenic formula. These formulas are made from broken down proteins, which are more easily digested and are less likely to cause a reaction of the immune system.
What types of formula can parents use for milk protein allergy?
Formulas used to treat milk protein allergy generally fall into 2 categories: extensively hydrolyzed formulas and amino acid-based formulas.
In extensively hydrolyzed formulas, the proteins are broken down into very small pieces that are easier to digest. These are usually more than 90% effective in reducing symptoms of milk protein allergy.
Amino-acid based formulas are made from amino acids, which are the building blocks of protein. These formulas can be used in infants who do not improve with extensive hydrolyzed formulas.
In most cases, infants with milk protein allergy should not use soy formulas or other mammalian milk-based formulas (e.g. goat’s milk formula) given high rates of cross-reactivity with cow’s milk proteins.
