Egg allergy: symptoms, diagnosis, baked egg, vaccines and outlook

Egg allergy means the immune system reacts to proteins in bird eggs, usually hen's eggs. Allergy UK explains that people allergic to hen's egg are at risk of reacting to eggs from other birds such as duck, quail or goose, and that egg allergy is different from allergy to chicken meat: most people with egg allergy can still eat chicken and other poultry. Fish and shellfish roe are classified under fish and shellfish allergy, not egg allergy.

The NHS lists eggs among the most common food allergens, alongside cows' milk, peanuts, soya, tree nuts, shellfish and wheat, and distinguishes a food allergy from a food intolerance, which tends to cause bloating and tummy pain a few hours after eating the food and does not involve the immune system in the same way.

Allergy UK describes four patterns. IgE-mediated allergy produces symptoms soon after exposure, often within minutes. Non-IgE-mediated allergy causes delayed symptoms, from hours to days later. Mixed allergy has both features. Food protein-induced enterocolitis syndrome (FPIES) is a rare and potentially severe non-IgE-mediated reaction with profuse vomiting and/or diarrhoea typically one to four hours after eating egg.

The timing matters for diagnosis. The NHS notes that symptoms of food allergy may appear straight after eating the food or days later, and that a food and symptoms diary can help work out the trigger. Reactions are not limited to eating: Allergy UK says touching egg or handling eggshells can cause a reaction, usually limited to the skin.

Allergy UK lists skin symptoms such as rash, redness, raised red bumps or hives, flares of eczema and swelling of the lips, eyes or face, and gut symptoms such as vomiting, stomach-ache or cramps and loose stools. Most reactions are mild or moderate. The NHS adds that symptoms can include itchy skin or a raised rash, swelling of the lips, face and eyes, coughing, wheezing or breathlessness, a runny or blocked nose, feeling sick, tummy pain and diarrhoea.

Severe reactions, called anaphylaxis, involve the airway, breathing or circulation. Allergy UK gives a swollen tongue, throat tightness or difficulty swallowing and speaking, a hoarse voice, a persistent cough or wheeze, noisy or difficult breathing, and in babies and young children becoming pale and floppy; older children and adults may feel dizzy, faint or lose consciousness.

• Mild to moderate: hives, itching, a flare of eczema, lip or face swelling, vomiting, tummy cramps, loose stools.

• Severe (anaphylaxis): difficulty breathing or swallowing, tongue or throat swelling, hoarse voice, pale and floppy child, collapse.

• Delayed or non-IgE: vomiting, diarrhoea, eczema flares or poor feeding hours to days after egg.

Allergy UK says babies with eczema are at higher risk of developing food allergies, probably because a weakened skin barrier allows food particles to enter through the skin and trigger the immune system. Other risk factors include already having another food allergy and a family history of eczema, hay fever, asthma or food allergy. The NHS also notes a slightly higher chance if you or a close family member have other allergies, asthma or eczema.

Allergy UK describes advice on early introduction of egg: for babies at higher risk, offering egg from around 4 to 6 months once solids have started can help reduce the risk of allergy, starting with small amounts and increasing gradually, and it says introducing egg after 12 months is linked with an increased risk of egg allergy. If a food causes a reaction, stop giving it and seek medical advice. Parents of a baby with moderate or severe eczema should discuss introduction with a health visitor or GP first.

Allergy UK says a diagnosis can often be made from a clear clinical history: what was eaten, how much, how it was cooked, how soon symptoms began and what they were. Testing is not always necessary, particularly for mild reactions. When the history is unclear or reactions are more severe, skin prick tests or blood tests may be recommended, though a positive test alone does not always confirm allergy and a negative test does not always rule it out.

The NHS says a GP who suspects a food allergy may refer to a specialist for tests, which can include a skin-prick test, blood tests, and a special exclusion diet to see whether symptoms improve. Allergy UK adds that referral to a specialist allergy clinic is sometimes needed, particularly for complex cases, children with several food allergies or people who have had severe reactions. Cutting foods out of the diet without advice is discouraged by the NHS.

Not everybody with egg allergy has to avoid every form of egg. Allergy UK says many people tolerate baked or well-cooked egg, such as egg baked into cake, and react only to lightly cooked or raw egg, because heat changes the structure of egg proteins. It cites around 80% of people with egg allergy tolerating well-baked egg in cake. The most sensitive people need to avoid all forms, and which category applies should be decided with a health professional.

For children who have had mild to moderate reactions, a professional may advise gradual reintroduction at home, often called an egg ladder, starting with well-cooked egg in small amounts and moving up. Children who have had severe reactions, or who are at higher risk, usually have reintroduction in hospital as a supervised oral food challenge. The NHS says people with a food allergy should check food labels and menus, tell others about the allergy, and carry adrenaline auto-injectors or a nasal spray if prescribed.

Vaccines are a common worry. Allergy UK says MMR is safe for all children with egg allergy, even severe allergy; the nasal flu vaccine is preferred for children and is very safe except in those with a history of reactions needing intensive care or who are immunocompromised, and most adults with egg allergy can receive flu vaccines. Anyone with egg allergy should see an allergy specialist before yellow fever vaccination.

The NHS says to call 999 if the lips, mouth, throat or tongue suddenly swell, if breathing is very fast or difficult, if the throat feels tight or swallowing is hard, if the skin, tongue or lips turn blue, grey or pale, if someone suddenly becomes very confused, drowsy or dizzy, if someone faints and cannot be woken, or if a child is limp, floppy or not responding normally. A swollen, raised or itchy rash may also be present.

If an adrenaline auto-injector or nasal spray has been prescribed, the NHS says to use it immediately and call 999 afterwards, even if the person seems to feel better. Do not drive to A&E. For a mild reaction, an antihistamine as advised by the allergy team and close observation are usual; if symptoms spread or breathing is affected, treat it as an emergency.

On the NHS, a health visitor or GP is usually the first contact for suspected egg allergy. Allergy UK notes that access to testing varies with local services and that a specialist clinic referral is sometimes needed. Children with severe eczema, several food allergies, a history of anaphylaxis or uncertain reactions are the ones most likely to be seen by a paediatric allergy service, where supervised challenges and written allergy action plans are provided.

Private paediatric or adult allergy clinics are also used, mostly for faster access to testing and review. The same principles apply: tests are interpreted alongside the history, and a positive result does not on its own mean egg must be avoided completely. Whichever route is used, discuss any test result with a clinician before cutting egg or other foods out of the diet, as the NHS advises against removing foods without medical advice.