Egg allergy is a common food allergy that primarily (but not exclusively) affects infants and children. In egg allergy, an inappropriate immune response is mounted against egg proteins following exposure, which rapidly produces symptoms like hives, facial swelling, and gastrointestinal distress. Dietary avoidance of egg is the mainstay of management, although most people will gain tolerance over time.
Egg allergy occurs due to an abnormal immune reaction following exposure to egg, and is one of the most common food allergies. This immune response is usually mediated by antibodies called immunoglobulin E (IgE) that inappropriately mark certain egg compounds as foreign invaders, initiating an immune attack that causes allergy symptoms like hives (urticaria), swelling of the face, and vomiting shortly after the exposure. Generally, egg allergy refers to hen’s eggs, but it may extend to the eggs of other birds like duck, goose, or quail.
Egg allergy usually occurs early in life after the initial introduction of eggs to the diet, but rarely, egg allergy may emerge in adulthood — and in these cases, it tends to be more severe and persistent. Egg allergy is estimated to affect 1 to 2% of children and just 0.1% of adults. Egg allergy that begins in childhood often resolves over time, with the median age of resolution being 6 to 9 years, and the majority of allergies being gone by age 16. Egg allergy is associated with an increased risk of other atopic conditions (i.e., IgE-mediated allergic conditions) , including other food allergies, eczema, allergic rhinitis, and asthma.
The most common symptoms of egg allergy include hives (urticaria) and facial swelling (angioedema) within minutes of exposure, and gastrointestinal symptoms (e.g., stomach pain, nausea, vomiting) within two hours of exposure. More severe symptoms, such as respiratory issues (e.g., cough, wheeze, change in voice pitch or hoarseness, shortness of breath), pale skin, and weakness can also occur, though less commonly. The severity of the reaction can depend on the amount of egg consumed and the degree to which the eggs are processed (raw or cooked, cooking duration and temperature, baked in a recipe with wheat, etc.).
Egg allergy can be diagnosed by a healthcare practitioner based on a clinical history of allergy symptoms beginning within minutes of egg consumption.
In some cases, the allergy may be confirmed by measuring egg-specific IgE using a skin prick test or blood test. However, these tests tend to have poor positive predictive value, meaning that sometimes the test will be positive for egg-specific IgE when a true egg allergy isn’t present. Therefore, a positive IgE test will only lead to a diagnosis if the person also reports allergy symptoms following egg consumption. Occasionally, an oral food challenge may be performed in a supervised setting where egg is administered and the person is monitored for an allergic reaction.
Avoiding eggs and egg whites is the mainstay of egg allergy management. As eggs are found in many different types of manufactured and home-cooked foods, it’s extremely important to read food labels and ask about ingredients. As a major food allergen, many countries require that “egg” be clearly indicated on the food label or ingredient list of manufactured foods, but this varies between regions. Additionally, egg cross-contamination (i.e., the presence of eggs in a food that doesn’t have egg as an ingredient) can occur in unpackaged grocery or buffet-style foods.
For managing an acute allergic reaction, second-generation antihistamines (e.g., loratadine, cetirizine) are recommended. First-generation antihistamines (e.g., diphenhydramine) are also effective but are more likely to cause side effects like drowsiness. For people with a previous severe reaction to egg, adrenaline (aka epinephrine) autoinjectors should be kept on hand in the event of an anaphylactic reaction.
A few supplements with known immune-modulating effects have been explored for their potential role in preventing food allergies — most notably, vitamin D, omega-3 fatty acids, probiotics, and prebiotics. Currently, results have been largely inconsistent, and there is insufficient evidence to support the use of any of these supplements for preventing egg allergy.
Once an allergy is confirmed, strict egg avoidance in the diet is recommended. Otherwise, there is currently little evidence to support particular dietary interventions for the prevention or management of egg allergy. However, there is evidence regarding cow’s milk allergy that suggests irregular ingestion in early life may promote allergy, supporting the idea that once a potentially allergenic food is successfully introduced into the diet it should be consumed regularly (a few times weekly) to prevent loss of tolerance. For short- or long-term formula-fed infants, replacing regular cow’s milk or soy formula with a formula that is partially or extensively hydrolyzed (proteins are broken down into smaller pieces) is likely not effective for preventing food allergies. Similarly, while breastfeeding is associated with a multitude of health benefits for the infant, it has not consistently been found to help prevent food allergies.
Egg oral immunotherapy is performed by an allergy specialist and involves the deliberate administration of slowly increasing amounts of egg over one to two years to an egg-allergic person to desensitize them. A 2018 Cochrane review found that egg oral immunotherapy was effective at building tolerance, with 82% of people able to tolerate a partial serving and 45% tolerating a full serving by the end of the treatment, compared to 10% of controls. However, 75% of people undergoing oral immunotherapy experienced allergy-related side effects, and 8.4% experienced anaphylaxis. This emphasizes the importance of oral immunotherapy only being done under the direct guidance and supervision of an allergy specialist.
Note that immunotherapy is generally not recommended for children with mild or moderate reactions, as the majority of them will “outgrow” their egg allergy by age 16 and require no intervention afterward.
Egg allergy, like other food allergies, occurs when there is a breakdown in immune system tolerance. Normally, the immune system is unresponsive to egg, but in egg allergy, the immune system becomes sensitized to egg protein and generates egg-specific IgE-antibodies. Upon re-exposure to egg, an IgE-mediated immune response occurs, which causes the release of histamine and other chemical mediators that create the symptoms of an allergic reaction. It’s not known why this loss of tolerance occurs in some people, but it likely involves a combination of genetic predisposition to immune sensitivity to eggs and environmental exposures that bring out such predispositions. Currently, there are two leading theories identified by the National Academy of Sciences, Engineering, and Medicine: The “microbial exposure hypothesis” suggests that reduced exposure to microbes early in life may hinder the development of the early immune system, leading to inappropriate reactivity; the “dual allergen exposure hypothesis” suggests that a damaged skin barrier (e.g., as seen in eczema) may allow for the absorption of food allergens through the skin before they have been introduced orally, leading to sensitization. Ultimately, more research is needed to fully understand what causes egg allergy, and the causes are likely multifactorial.
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