Cow’s Milk Allergy: Symptoms & Diagnosis

Cow’s Milk Allergy: Symptoms & Diagnosis

Cow’s milk allergy is a common diagnosis in infants and children. It characteristically presents as an allergic reaction to the protein found in cow’s milk. Cow’s milk allergy manifests as a variety of symptoms and signs which commonly develop in infants and can regress by the age of 6. It can be a source of parental and family stress due to a milk-free diet and can lead to a subsequent nutritional deficiency if not treated appropriately.

Food allergies stem from the host’s immune system. If an individual has an allergy to milk, the body’s immune system responds to a specific milk protein, triggers an immune response, and attempts to neutralize the triggering protein. The next time that the body comes into contact with the protein, the immune response recognizes the protein. It triggers the immune system to mount a response, including the release of histamine and other immune mediators. This release of chemicals causes the signs and symptoms of cow’s milk allergy.

It is difficult to determine the exact prevalence of cow’s milk allergy due to a lack of a precise criterion for diagnosis. Often the term allergy is interchanged with intolerance or hypersensitivity. In the developed world, the prevalence appears to be 2 to 3% in infants. There is no evidence that prevalence is increasing, and parents perceive cow’s milk allergy more frequently than can be proven with an oral challenge. By the age of 6, the prevalence has fallen to less than 1%.

Cow’s milk contains more than 20 protein fractions. The significant allergens belong to casein protein (alpha-s1-, alpha-s2-, beta-, and kappa-casein) and whey proteins (alpha-lactalbumin and beta-lactoglobulin). Most individuals with cow’s milk allergies have a sensitivity to both caseins and whey proteins. Immune-mediated adverse food reactions classify into two primary categories: IgE-mediated, non-IgE-mediated. A non-IgE mediated mechanism most frequently causes cow’s milk allergy.

Typically the presence of cow’s milk allergy appears within the first few months of life and usually before six months. Symptoms can present a few days or weeks after the ingestion of cow’s milk protein. The symptoms can vary from diarrhea and emesis to life-threatening anaphylaxis. In cases that involve the GI tract, the child can become dehydrated and exhibit a failure to thrive.

Cow’s milk allergy reactions classify into rapid onset; usually, IgE mediated, where symptoms occur within an hour after ingestion, and slow onset, non-IgE mediated, where symptoms take hours or days to present.

Rapid onset symptoms can include:

  • Urticaria/hives
  • Wheezing
  • Itching or a tingling feeling around the mouth or lips
  • Angioedema: swelling of the lips, tongue, or throat
  • Coughing or shortness of breath
  • Vomiting
  • Anaphylaxis

Slow onset symptoms can include:

  • Diarrhea
  • Hematochezia
  • Abdominal cramps
  • Colic

Anaphylaxis is a medical emergency requiring treatment with an epinephrine shot and evaluation in the emergency room. Signs and symptoms start soon after milk consumption and can include:

  • Increased work of breathing
  • Constriction of airways
  • Swollen throat
  • Facial flushing
  • Itching

The clinician must recognize the difference between milk allergy and milk intolerance. The major difference is that intolerance does not involve the immune system. Common symptoms of milk intolerance include gas, bloating, or diarrhea after ingesting milk. The treatment of intolerances and allergies is different.


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