Eggs are very versatile foods and for many people an inherent part of the diet. However, they also are one of the most common allergy triggers worldwide.
Along with milk allergy, egg allergy is the most common allergy in childhood. Approximately 4 to 6 percent of children are affected. The egg allergy often develops during the first two years of life and disappears by itself during school age. Adults are rarely affected. In affected persons, eggs can cause allergic reactions even in smallest quantities, leading to symptoms such as nausea, diarrhea, itching, swelling, rashes, shortness of breath or even anaphylactic shock. Triggers of the reaction are allergenic proteins in the egg.
There are more than 40 different proteins in a hen’s egg, of which five are of clinical relevance:
- Ovomucoid (Gal d 1): Along with ovalbumin, ovomucoid is the main allergenic protein in eggs. It is of high allergenic potential and heat-resistant. This means that people allergic to ovomucoid tolerate neither raw nor cooked or fried eggs.
- Ovalbumin (Gal d 2): Ovalbumin is the major allergen in eggs by volume. It is heat-labile and decomposes at around 80°C. People who are allergic to this protein often tolerate hard-boiled eggs or cake.
- Ovotransferrin (Gal d 3): Ovotransferrin, also referred to as conalbumin, is an iron-binding glycoprotein and decomposes at around 60°C.
- Lysozyme C (Gal d 4): Lysozymes have an antimicrobial effect which is why they are widely used as a preservative in foods.
- Livetin: Alpha-livetin is the major allergen in the egg yolk. It shows cross-reactivity with serum albumin and usually triggers egg allergies in adults.
Cross-reactions between the different allergens in a hen’s egg and with eggs of other birds (e.g. quail eggs, goose eggs, duck eggs or seagull eggs) are possible. Allergy sufferers should get their tolerance tested by an allergist before consumption. A relatively rare condition is the so-called “bird-egg syndrome” that usually affects bird owners. Affected persons develop an allergy against the bird’s feathers and excrements. As the disease progresses, cross-sensitivities with chicken egg and meat can occur.
The most important part of allergy treatment is avoiding the allergenic substances in the diet. In order to protect allergy sufferers from unintentional consumption, eggs must be labelled as an allergen in most countries. To ensure correct labelling in the food industry, test systems to determine the egg content in foods are available.