Cow’s Milk Protein Allergy (CMPA) is one of the most common food allergies affecting infants. This condition involves an adverse immune system reaction to cow’s milk proteins, which can cause distress and impact an infant’s health. While breastfeeding offers a protective effect against many illnesses and allergies, it does not provide complete immunity from CMPA. Recognizing that this allergy can occur even in exclusively breastfed babies is an important first step toward accurate diagnosis and effective management.
Understanding Cow’s Milk Protein Allergy
Cow’s Milk Protein Allergy is an immune-mediated hypersensitivity reaction to the proteins in cow’s milk, primarily casein and whey. It differs fundamentally from lactose intolerance, which is a digestive issue caused by the inability to break down lactose. CMPA involves the body’s immune system mistakenly identifying the milk proteins as a threat, triggering an allergic response.
After the mother consumes dairy products and digests cow’s milk, fragments of the proteins, such as beta-lactoglobulin (β-LG), are absorbed into her bloodstream. These protein fragments then pass into the mammary glands and are excreted into the breast milk. Though the concentration of these proteins in breast milk is extremely low—up to 100,000 times lower than in cow’s milk itself—it is sufficient to trigger an allergic reaction in a sensitized infant.
Prevalence Among Breastfed Infants
The incidence of CMPA in the general infant population is estimated to range between 2% and 7.5% in the first year of life. However, the rate is markedly lower among infants who are exclusively breastfed, affecting approximately 0.5% to 1% of this group.
This lower prevalence suggests that exclusive breastfeeding offers a protective effect compared to formula feeding, which exposes the infant to a much larger load of cow’s milk protein. Despite the lower risk, CMPA remains a possibility, and its diagnosis can be complicated because many common infant symptoms mimic those of an allergy. The allergy is often over-diagnosed, which can lead to unnecessary maternal dietary restrictions.
In breastfed infants, the allergic reaction is typically a non-IgE-mediated (delayed) response, rather than an IgE-mediated (immediate) one. Immediate, IgE-mediated reactions (involving Immunoglobulin E) are rare. The non-IgE type involves other parts of the immune system and is characterized by symptoms that appear hours or even days after protein exposure, making it more challenging to link to the mother’s diet.
Recognizing the Signs of CMPA
CMPA symptoms can be diverse and often affect multiple body systems. Non-IgE-mediated reactions, the most common type in breastfed infants, often manifest as chronic, delayed symptoms that can easily be mistaken for typical infant issues. Parents should observe for a pattern of symptoms rather than a single isolated event.
Gastrointestinal and Behavioral Symptoms
Gastrointestinal symptoms are frequently reported, including chronic reflux or frequent regurgitation that does not respond to standard treatments. Changes in stool are another significant sign, such as persistent diarrhea, constipation, or the presence of visible mucus or blood streaks. Prolonged periods of inconsolable crying or colic that lasts more than three hours a day, three days a week, for over three weeks may also be a symptom.
Skin and Respiratory Symptoms
Skin issues commonly include persistent or severe eczema, hives, or a rash that fails to clear up with typical care. Infants may also develop respiratory symptoms such as persistent congestion, chronic runny nose, or wheezing unrelated to an infection. Failure to thrive, or poor weight gain, is a serious sign that requires immediate medical attention. If immediate symptoms like facial swelling or sudden difficulty breathing occur, this suggests a severe, IgE-mediated reaction that requires emergency care.
Dietary Management While Breastfeeding
The optimal goal for an infant with CMPA is to continue breastfeeding while managing the allergen exposure. The standard management protocol for a suspected allergy is a diagnostic maternal elimination diet. This involves the mother completely removing all sources of cow’s milk protein from her diet.
Strict avoidance of all milk, butter, cheese, and milk solids is necessary, as dairy ingredients can be hidden in many processed foods. A healthcare provider or dietitian should supervise this elimination period to ensure the mother’s nutritional needs are met. Mothers on this diet may need a supplement of 1000 mg of calcium and 10 micrograms of vitamin D daily, since dairy is a primary source of these nutrients.
Symptom improvement is typically seen within two to four weeks of starting the elimination diet. If symptoms resolve, a formal diagnosis is confirmed by a supervised reintroduction, or challenge, of cow’s milk into the mother’s diet to see if the symptoms return. If symptoms do not improve after the initial elimination period, CMPA is unlikely to be the cause, and the mother should resume her normal diet to avoid unnecessary restriction.