Egg Allergy

Egg allergy is an immune reaction to proteins in hen's egg, mainly ovomucoid and ovalbumin in egg white. It is the second commonest food allergy in young children, and most children outgrow it.

Pathophysiology. Most disease is IgE-mediated, with reactions within minutes to 2 hours of eating egg. Non-IgE forms (allergic proctocolitis, FPIES, eosinophilic oesophagitis) cause delayed gastrointestinal symptoms.

Ovomucoid is heat and digestion stable, so children allergic to it react to baked egg as well. Children sensitised mainly to heat labile ovalbumin often tolerate egg baked in cakes or biscuits.

It affects roughly 1 to 2% of young children. Persistence is more likely with high egg specific IgE, ovomucoid sensitisation, reactions to baked egg, and other atopic disease.

• Urticaria, angio oedema and flushing within minutes of eating egg
• Vomiting, abdominal pain, diarrhoea
• Wheeze, cough, rhinitis, throat tightness
• Anaphylaxis, less often than with peanut or tree nut
• Eczema flares in infants with sensitisation
• Delayed vomiting, pallor and lethargy 1 to 4 hours after egg (FPIES)
• Contact urticaria from handling egg

• History: form of egg (raw, lightly cooked, baked), amount, timing and route of reaction, and eczema.
• Skin prick test and specific IgE to egg white, egg yolk and ovomucoid: a wheal of 7 mm or more in infants, or specific IgE to egg white over 7 kU/L, makes a reaction likely. A positive result alone is not proof, and a negative result does not exclude non-IgE disease. Ovomucoid specific IgE predicts reactions to baked egg.
• Supervised oral food challenge (baked egg first, then heated or lightly cooked egg) is the reference test, and is avoided after a recent severe reaction.
• Growth chart, and eosinophilic oesophagitis workup if feeding is difficult.

Differential diagnosis.

• Egg intolerance and food aversion
• Other food allergy (cow's milk, peanut, wheat)
• Eczema without food allergy
• Eosinophilic oesophagitis and FPIES
• Chicken meat or feather sensitisation (bird egg syndrome)
• Food poisoning

• Avoidance of the forms of egg that cause reactions. Read labels for egg, albumin, ovalbumin, lysozyme and lecithin from egg.
• Baked egg: if a challenge shows tolerance, include baked egg regularly, since this helps resolution. Start with a supervised challenge in children with ovalbumin dominant sensitisation.
• Mild to moderate reactions: cetirizine (children 1 to 5 years 2.5 mg twice daily; 6 to 11 years 5 mg twice daily; over 12 years and adults 10 mg once daily).
• Anaphylaxis: adrenaline 0.01 mg/kg intramuscularly (maximum 0.5 mg) into the anterolateral thigh, repeated after 5 minutes if no improvement, plus oxygen, intravenous fluids and observation for at least 6 hours.
• Adrenaline auto injector for children with a history of systemic reactions, asthma or ovomucoid sensitisation: 150 microgram for 7.5 to 25 kg, 300 microgram for 25 to 50 kg, 500 microgram for over 50 kg, with a written action plan and training of carers and school.
• Reintroduction: a graded baked egg ladder, then lightly cooked egg, with supervised challenge every 6 to 12 months while tolerance is uncertain.
• Vaccines: measles-mumps-rubella vaccine and inactivated influenza vaccine are safe in egg allergy. Yellow fever vaccine contains egg protein and needs specialist assessment before it is given.
• Egg oral immunotherapy is a specialist option for persistent allergy with a risk of reactions.

Special groups.

• Infants with severe eczema: early introduction of cooked egg (well cooked, for example hard boiled or baked) from 4 to 6 months reduces the risk of allergy, after allergy assessment when eczema is severe.

Monitoring. Growth at each visit. Review every 6 to 12 months to plan challenge or reintroduction. Check that auto injectors are in date and dosed for current weight.

Referral and escalation. Refer to paediatric allergy for anaphylaxis, reactions to baked egg, multiple food allergy, or asthma with egg allergy. Emergency for anaphylaxis, or repeated vomiting with pallor and lethargy.