What is the best course of action for a healthy, breastfeeding infant less than 6 months old with no known allergies, who develops urticaria (hives) after introducing formula to their diet?

Management of Hives After Introducing Formula to a Breastfeeding Infant

Immediately discontinue the formula and continue exclusive breastfeeding while eliminating all cow's milk and dairy products from the mother's diet, as this represents a likely IgE-mediated cow's milk protein allergy. 1, 2

Immediate Actions

Stop the formula immediately and do not reintroduce it without medical supervision, as urticaria (hives) occurring within minutes to hours after formula introduction indicates an IgE-mediated allergic reaction to cow's milk protein. 3

• Continue breastfeeding exclusively while the mother eliminates all cow's milk and dairy products from her diet, including milk, cheese, yogurt, butter, and hidden sources in processed foods. 1, 2
• Cow's milk proteins transfer through breast milk in sufficient quantities to cause allergic reactions in sensitized infants, so maternal dietary elimination is essential. 1, 2

Expected Timeline for Improvement

• Symptoms typically improve within 1-2 weeks of strict maternal dietary elimination, though improvement may take up to 4 weeks depending on the severity of the allergic manifestation. 1, 2
• Document symptom resolution during this elimination period to confirm the diagnosis. 3

Nutritional Support for the Mother

• Refer to a registered dietitian to ensure the mother's diet remains nutritionally adequate while avoiding all cow's milk proteins. 1, 2
• Provide calcium supplementation and address other nutritional considerations to maintain maternal health during breastfeeding on a restricted diet. 1, 2

If Symptoms Persist or Breastfeeding Cannot Continue

• If symptoms persist after 2 weeks of strict maternal elimination, consult an allergy specialist for further evaluation. 1
• If the mother cannot maintain the elimination diet or breastfeeding is not possible, switch to an extensively hydrolyzed formula (eHF) as first-line treatment, which has an 80-90% success rate. 2, 4
• For severe reactions or if the infant fails to respond to extensively hydrolyzed formula, use an amino acid-based formula (AAF). 1, 2, 4

Critical Pitfalls to Avoid

• Do not use soy formula as a first-line alternative, as there is a 20-40% cross-reactivity risk with cow's milk protein allergy. 2, 4
• Do not use goat's milk or sheep's milk as alternatives, as they have high protein homology with cow's milk and are not suitable substitutes. 1, 4
• Do not discontinue breastfeeding prematurely when maternal dietary elimination can effectively manage symptoms. 1, 2
• Avoid implementing highly restrictive maternal diets that eliminate multiple foods beyond cow's milk unless other allergies are confirmed, as this may compromise maternal nutrition. 1, 2

Formal Diagnosis and Testing

• Eliminate the suspected formula for 2-8 weeks before considering any oral food challenge, with the length depending on the type of reaction (urticaria requires shorter elimination than chronic gastrointestinal symptoms). 3
• Oral food challenges should only be performed by medical personnel with experience in managing food allergies, with treatment for anaphylaxis immediately available. 3
• Do not perform widespread skin prick tests or specific IgE tests for screening purposes, as they have poor predictive value and lead to unnecessary dietary restrictions. 2

Long-Term Management and Reintroduction

• Attempt reintroduction of cow's milk protein under medical supervision typically after 6-12 months of elimination, with timing individualized based on initial symptom severity. 1, 2
• Most children eventually tolerate cow's milk, with tolerance often developing during childhood, though high initial specific IgE levels, additional atopic disease, or multiple food allergies are risk factors for persistence. 3
• Do not delay introduction of other solid foods beyond 4-6 months of age in this infant with cow's milk allergy. 2