Food Allergy in Children
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Direct answer
Food allergy occurs when the immune system reacts abnormally to a food protein, most often through IgE-mediated mechanisms that cause urticaria, angioedema, vomiting or anaphylaxis within minutes to two hours. Cow's milk, hen's egg, peanut, tree nut, fish, shellfish, wheat, soy and sesame cause most reactions in children. Oral food challenge remains the diagnostic gold standard, and early introduction of allergenic foods is advised for many infants.
What you must remember
- IgE-mediated reaction: immediate onset within minutes to two hours; urticaria, wheeze, vomiting or anaphylaxis, supported by specific IgE or skin prick tests.
- Non-IgE reaction: delayed or mixed, including food protein-induced enterocolitis syndrome (FPIES) and food protein-induced allergic proctocolitis in breastfed infants.
- Common allergens: cow's milk, hen's egg, peanut, tree nuts, fish, shellfish, wheat, soy and sesame.
- Natural history: cow's milk and egg allergy often resolve by school age, while peanut, tree nut, fish and shellfish allergy usually persist.
- Oral food challenge: supervised, graded doses in a monitored setting; used when history and tests are equivocal.
- Anaphylaxis: intramuscular adrenaline 0.01 mg/kg (maximum 0.5 mg) into the anterolateral thigh, repeated if needed.
- Early introduction: peanut and egg introduced alongside breastfeeding around four to six months reduces peanut allergy in high-risk infants.
- Sensitisation is not allergy: a positive specific IgE shows sensitisation; clinical allergy needs a convincing history or a positive challenge.
Diagnosing and managing a suspected food reaction
A 3-year-old develops urticaria and vomiting within 20 minutes of eating a peanut-containing biscuit. The work-up separates an IgE-mediated reaction from a delayed syndrome, because the testing and advice differ.
- Take a precise history. Record the food, the amount, the timing and any prior reaction; onset within minutes to two hours suggests IgE mediation.
- Assess severity. Look for respiratory compromise, hypotension or multi-system involvement, which define anaphylaxis.
- Send sensitisation tests. Specific IgE or skin prick tests support the diagnosis, but a negative result often helps rule out IgE-mediated allergy.
- Confirm with oral food challenge. A graded, supervised challenge is the gold standard when the history and tests are unclear.
- Prescribe an emergency plan. Confirmed severe allergy needs an adrenaline auto-injector and a written plan for family and school.
- Review periodically. Milk and egg allergy are re-challenged over time; peanut and tree nut allergy are re-tested only under specialist care.
Where the exam tries to catch you
Allergy vignettes often reward a clear separation of IgE and non-IgE patterns.
- Trap: avoiding peanut altogether in an infant with eczema because of family history. Correct: early introduction is advised for infants with mild to moderate eczema, while severe eczema or egg allergy needs specialist assessment first.
- Trap: labelling a child allergic on a positive specific IgE alone. Correct: sensitisation is not clinical allergy; a convincing history or a positive oral challenge confirms it.
- Trap: treating FPIES as IgE anaphylaxis. Correct: FPIES gives repetitive vomiting and lethargy one to four hours after ingestion with negative IgE tests, and is managed by avoidance and fluids.
Frequently asked questions
Which investigation is the diagnostic gold standard for food allergy in children?
Oral food challenge is the diagnostic gold standard for food allergy in children. It is performed as a graded, supervised exposure to the suspected food, with emergency treatment immediately available if a reaction occurs.
Which foods most commonly cause IgE-mediated food allergy in children?
Cow's milk, hen's egg, peanut, tree nuts, fish, shellfish, wheat, soy and sesame most commonly cause IgE-mediated food allergy in children. Cow's milk and egg allergy are most frequent in infancy, while peanut and tree nut allergy tend to persist.
What is the emergency dose of intramuscular adrenaline for anaphylaxis in a child?
The emergency dose of intramuscular adrenaline for anaphylaxis in a child is 0.01 mg/kg, with a maximum single dose of 0.5 mg. It is given into the anterolateral thigh and can be repeated at five-minute intervals if symptoms persist.
When should peanut be introduced to an infant with eczema?
Peanut should be introduced to an infant with mild to moderate eczema around four to six months, alongside breastfeeding and continued normal feeding. Infants with severe eczema or known egg allergy need specialist assessment, often with testing, before introduction.
Which food allergies usually resolve by school age?
Cow's milk allergy and hen's egg allergy usually resolve by school age in most children. Peanut, tree nut, fish and shellfish allergies more often persist into adult life and need long-term avoidance and planning.