Quick Answer
Cow's milk allergy is the most common food allergy in infants, affecting 2–3% of babies. It is caused by IgE antibodies to milk proteins, primarily casein and whey. Symptoms range from hives and vomiting to anaphylaxis. Most children outgrow cow's milk allergy by age 5, but strict avoidance and epinephrine prescription are required in the interim.
IgE vs Non-IgE Milk Reactions
Cow's milk allergy manifests in two distinct immune mechanisms. IgE-mediated milk allergy produces rapid symptoms (within 30 minutes) including urticaria, angioedema, vomiting, and anaphylaxis — these reactions require epinephrine prescription and strict avoidance. Non-IgE-mediated milk hypersensitivity (including FPIES, allergic proctocolitis, and food-induced allergic enteropathy) produces delayed gastrointestinal symptoms without hives or respiratory involvement.
FPIES (Food Protein-Induced Enterocolitis Syndrome) from cow's milk causes profuse projectile vomiting 1–4 hours after feeding, often with pallor and lethargy. It is non-IgE-mediated, so skin prick tests and IgE blood tests are negative. Diagnosis is clinical and through supervised oral challenge. FPIES typically resolves by age 3–5.
Milk Allergen Proteins: Casein and Whey
The two major milk protein fractions are casein (80% of total protein) and whey (20%). Casein proteins (αs1-casein, αs2-casein, β-casein, κ-casein) are highly heat-stable — they survive cooking and pasteurization and are present in cheese, yogurt, and dried milk. Casein sensitization typically indicates more severe, persistent milk allergy.
Whey proteins (β-lactoglobulin, α-lactalbumin, bovine serum albumin, lactoferrin) are variably heat-labile. Some milk-allergic children tolerate extensively baked (heated to 180°C) milk products because heating denatures whey proteins without fully denaturing casein. Patients who tolerate baked milk are more likely to outgrow milk allergy than those who react to baked forms.
Formula Alternatives for Milk-Allergic Infants
For breastfeeding mothers, elimination of dairy from the mother's diet often resolves cow's milk protein reactions in exclusively breastfed infants. For formula-fed infants diagnosed with IgE-mediated cow's milk allergy, extensively hydrolyzed casein formulas (Nutramigen, Alimentum) are first-line — they break milk proteins into small peptides that are less likely to trigger IgE-mediated reactions.
Amino acid-based (elemental) formulas (Neocate, EleCare) are used for infants who react to hydrolyzed formulas or who have severe eosinophilic disease. Soy formula is not recommended for infants with IgE-mediated cow's milk allergy due to 30–40% cross-sensitization to soy. Sheep, goat, and buffalo milk contain proteins that cross-react with cow's milk and are not safe substitutes.
Milk Allergy vs Lactose Intolerance
Cow's milk allergy and lactose intolerance are entirely distinct conditions and are frequently confused. Milk allergy is an immune-mediated reaction to milk proteins (casein, whey) that can cause anaphylaxis and requires strict avoidance. Lactose intolerance is a non-immune digestive deficit of lactase enzyme, causing gas, bloating, and diarrhea — symptoms that are uncomfortable but not dangerous.
Lactase supplements allow most lactose-intolerant individuals to consume dairy products. Aged cheeses and yogurt have naturally lower lactose and are often tolerated. Lactose intolerance does not require epinephrine, does not prevent skin testing, and does not place the patient at anaphylaxis risk. Patients incorrectly labeled as 'milk allergic' when they have lactose intolerance may unnecessarily restrict their diet.
Key Takeaways
- Milk allergy affects 2–3% of infants and is the most common early food allergy.
- IgE-mediated reactions are rapid and can cause anaphylaxis; non-IgE reactions (FPIES) cause delayed vomiting.
- Casein is heat-stable; whey is partially heat-labile — baked milk tolerance predicts outgrowing the allergy.
- Extensively hydrolyzed formula is first-line for milk-allergic formula-fed infants.
- Milk allergy and lactose intolerance are completely distinct — confusion between them is common but consequential.
Related Guide
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