Cow's milk allergy is the most common food allergy in young children, affecting about two percent of children under four years of age. It is the third most common food, after peanut and tree nuts, responsible for food-induced anaphylaxis in pediatric population. This food allergy presents with a wide range of clinical syndromes due to immunologic responses to cow's milk proteins that can be immunoglobulin (Ig)E- and/or non-IgE-mediated. IgE-mediated food-triggered reactions generally occur immediately, within minutes to two hours after ingestion. These reactions can present with skin, upper and lower respiratory tract, gastrointestinal tract, and/or cardiovascular signs and symptoms.

All milk proteins are potential allergens. Cow's milk contains casein and whey proteins that account for approximately 80 and 20 percent of total protein, respectively. Cooking diminishes the allergenicity of whey proteins, presumably by denaturation of heat-sensitive proteins. This may explain why extensively heated milk (eg, milk in baked goods) is better tolerated by many patients. Similarly, yogurt cultures, which ferment and acidify milk, diminish the amount of intact whey protein in milk and may result in tolerance of yogurt-based dairy products by individuals with cow’s milk allergy exclusively sensitized to whey proteins.

Sample conditions affected by milk allergy:

Atopic dermatitis (eczema) — Food allergy plays a pathogenic role in a subset of patients, primarily infants and children, with atopic dermatitis.

Allergic gastrointestinal disorders — Milk is also among the major allergens identified in allergic eosinophilic esophagitis. Patients with this disorder have symptoms suggestive of gastroesophageal reflux, but are unresponsive to conventional reflux therapies. Other presenting symptoms include feeding disorders, vomiting, and abdominal pain. Patients with allergic eosinophilic gastroenteritis may have symptoms of abdominal pain, nausea, vomiting, diarrhea, or weight loss.

Gastroesophageal reflux — Symptoms in gastroesophageal reflux may be associated with cow's milk allergy.

Constipation — Cow's milk allergy/intolerance has been suggested as a cause of constipation in infants and children, especially in those with chronic constipation.

The diagnosis of cow’s milk allergy is based upon the history and laboratory testing. The gold-standard diagnostic procedure may include elimination of the suspected food, challenge, and re-elimination. In breastfed infants, this includes a maternal exclusion diet avoiding cow's milk protein. In formula-fed infants, the use of either extensively hydrolyzed or amino acid-based infant formulae is recommended. If minimal to no improvement is noted on a milk avoidance diet, the food in question is not responsible for symptoms, the diet has not been restricted enough, or the patient may have multiple food allergies and additional foods may be considered suspicious. Measurement of cow's milk-specific IgE can aid in the diagnosis of IgE-mediated cow’s milk allergy and may eliminate the need for oral food challenges.

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