Cow’s Milk Allergy in infants (CMPA), explained by a pediatric allergist
Written by Dr. Relan, pediatric allergist and clinical immunologist
Cow's milk allergy is complicated. There are many proteins in cow's milk but the most commonly implicated ones are whey and casein. Recall, an allergic reaction is typically an immune response to the protein component of a food. There is such a thing as lactose intolerance which is when the body cannot break down the milk sugar lactose because of a deficiency of the enzyme which breaks it down, called lactase. There are also variable amounts of fat in milk, depending on the percentage purchased and consumed; some people find it harder to digest foods containing higher levels of milk fat.
When a person has a hard time tolerating cow's milk protein, first it needs to be clarified whether the allergic reaction was IgE mediated or non-IgE mediated. There are often clues in the history, with timing of what happened and which symptoms developed being most helpful. When a reaction is IgE mediated it occurs within minutes to two hours and generally speaking, may be life threatening. This is the allergy that most of us worry about - with immediate rashes (hives), wheezing, coughing, runny nose, vomiting. Thankfully, anaphylaxis in infants is rare.
Non-IgE mediated reactions on the other hand is a delayed reaction, occurring up to hours or days later. In these cases, infants will present with GI symptoms (like vomiting, diarrhea, mucous in the stool, blood in the stool, belly aches), irritability (lots of crying, fussing, colic-like) and alongside it rashes (eczema), poor growth, sometimes even respiratory symptoms. There can be many causes of blood in the stool, including infection, blockage in the gut, or minor irritation around the anus so do not automatically assume allergy. Always check with your baby's doctor with any concerns.
The most common milk allergy of infancy used to be referred to as CMPA but is now most commonly called CMPI, with the "i" standing for intolerance. In majority of the cases, CMPA or CMPI is typically referring to "food protein-induced allergic proctocolitis" (FPIAP) which is a scenario where an infant cannot digest a food protein (ie, cow's milk, soy) well. This may be via formula or the maternal diet via breastmilk. When the symptoms are limited to vomiting and/or diarrhea occurring 2 to 4 hours after drinking milk, it usually refers to FPIES which states for "food protein induced enterocolitis syndrome". There is also an entity called food protein-induced enteropathy where a larger portion of the GI tract gets involved and the symptoms are more severe. Another cause of a delayed reaction to milk are the eosinophilic gut diseases but these are extremely rare in infancy.
In the case of an IgE mediated cow's milk allergy, milk from other mammals like goat, sheep, buffalo also needs to be avoided. Milk from equine such as donkey or horse are only 10% cross reactivity and thus better tolerated but more difficult to find. Some people with a cow's milk allergy (up to 10%) also have to take caution with ingestion of beef as there are similar proteins in cow's milk and beef. The good news is that up to 70% of people with a cow's milk allergy can tolerate it in small amounts if baked into foods like cake or muffin, and some can even tolerate it in well heated cheese. This is because in the process of baking, the strong heat (versus that on a stove top) and duration in the oven changes in the milk protein structure. Our immune system is that specific - it can tell the difference between heated and unheated milk protein! Please discuss all of this with an allergist and review the introduction of new foods under their guidance only.
Regardless of the type of milk allergy present, avoidance is typically a must. If an infant is formula fed, they may need to switch to a "hypoallergenic" one where there is an extensive casein hydrolysate or an "elemental" one which is amino-acid based. The other option is to try soy formula but this too sometimes causes a protein intolerance. If the infant is breastfed, sometimes a maternal elimination of milk helps with eventual gradual reintroduction to see if symptoms reoccur or if small amounts are tolerated. CMPA or CMPI is typically outgrown by 1 year of age; IgE mediated cow's milk allergy takes longer with 50-80% resolving by age 5 (and the majority by adolescence).
Reading labels can be challenging as milk can be found in "non-dairy" products including non-dairy creamers, contaminated via shared surfaces like deli meat (where cheese is cut with the same slicer), and sometimes in seafood processing. Milk can also be present in other foods marketed for pets and even non-food stuff such as medications, cosmetics, nutritional supplements.
When it comes to actually managing an allergy, finding a pediatric board certified allergist you trust is important - start with your child's pediatrician for referral or check out "AAAAI find an allergist" or "ACAAI find an allergist". There are also some helpful websites such as Kids with Food Allergies, Food Allergy Research and Education, and the Asthma and Allergy Foundation of America.
Best wishes,
Dr. Relan
Manisha Relan, MD is a double board-certified pediatric allergist and clinical immunologist in New York. Dr. Relan states her most important role is being a mom! She is an advocate for food allergy prevention (to the best of our ability) and plant-based eating. She practiced baby-led feeding with both of her sons, albeit slow to start with her eldest, but hopes you will find the confidence and all the information/support in this book to do so, too!
Instagram @pedsallergymd
