OVERVIEW

What is egg allergy?

Egg allergy is a common food allergic reaction in daily life, characterized by the body's abnormal immune response to proteins in eggs ^[1].

The occurrence of egg allergy is associated with various factors, such as genetics, initial age of exposure to eggs, route and dosage of exposure, body reactivity, development of gastrointestinal mucosa, viral infections, and stability of gut microbiota ^[2].

Is egg allergy common?

Egg allergy is very common in daily life.

Eggs are one of the eight major food allergens (milk, eggs, peanuts, fish, crustacean shellfish, soybeans, wheat, and tree nuts) identified by the Food and Agriculture Organization/World Health Organization (FAO/WHO) that cause food allergies in humans.

The United States and the European Union mandate that eggs must be labeled as an allergen either immediately after or near the ingredient list, with the same font size as the ingredient list, or marked in parentheses next to the relevant allergen in the ingredient list ^[3].

In recent years, the number of food allergy cases has been increasing, and the incidence of allergies has shown a yearly upward trend. It is reported that 22% of the world's population experiences varying degrees of allergic symptoms.

Foreign epidemiological surveys indicate that approximately 2.5% of adults and 6%–8% of children are allergic to certain foods. Among these, egg allergy accounts for 12% of adult food allergies and 35% of childhood food allergies, with infants under one year old being particularly susceptible ^[1,4].

Some adults with congenital genetic defects (hereditary allergies) may also be allergic to eggs ^[5].

SYMPTOMS

What are the symptoms of egg allergy?

Food allergies can trigger a range of allergic reactions, from mild discomfort to life-threatening conditions ^[2,4,6,7,8].

Symptoms of egg allergy often appear within minutes or hours after ingestion and can affect the skin, respiratory tract, digestive system, and more.

• Skin symptoms: Mainly include hives, eczema, and skin redness;
• Oral symptoms: Redness and swelling of the mouth and lips;
• Respiratory symptoms: Primarily rhinitis, nasal congestion, and allergic respiratory diseases such as bronchial asthma;
• Gastrointestinal symptoms: Such as nausea, vomiting, diarrhea, and stomach cramps. Gastrointestinal discomfort may also cause drowsiness or fatigue and even severe angina in extreme cases;

If allergic symptoms persist for an extended period, severe cases may lead to anaphylactic shock.

What are the risks of egg allergy?

Beyond causing clinical symptoms of varying severity in different body parts, egg allergy can also impact children's physical and psychological well-being.

Children are a high-risk group for egg allergy. Severe itching, skin lesions, and other allergic reactions may lead to sleep disturbances, delayed growth, emotional distress, low self-esteem, and social withdrawal ^[7].

As children grow older, egg allergy tends to gradually improve, reducing its associated risks.

CAUSES

What causes egg allergy?

The reason is that the human immune system rejects the egg white proteins entering the body, triggering a series of immune reactions ^[2,9].

The allergens in eggs are mainly found in the egg white. There are five major protein components in egg white that can bind to human serum IgE and cause allergic reactions: ovomucoid, ovalbumin, ovotransferrin, lysozyme, and ovomucin.

Ovomucoid is the most characteristic allergen in egg white, accounting for about 11% of the total egg white protein. Compared to other egg white proteins, ovomucoid is the most allergenic protein detected in the serum of egg-allergic patients.

Who is most prone to egg allergy?

Egg allergy is most common in children under 3 years old.

Because the intestinal mucosa and gastrointestinal barrier of infants and young children are not fully developed, incompletely digested antigenic substances (such as eggs) entering the body are more likely to cause allergic reactions. This is also the main reason why children and infants are prone to other food allergies ^[8].

Globally, approximately 0.5% to 2.5% of children are allergic to eggs ^[10]. Egg allergy cannot be cured but tends to improve with age.

DIAGNOSIS

Which department should be consulted for egg allergy?

First, the Allergy or Immunology Department is recommended.

If the local hospital does not have an Allergy or Immunology Department, patients can visit the corresponding department based on the location of allergic symptoms. For example, dermatology for skin symptoms (such as hives or eczema), respiratory medicine for allergic asthma, and otolaryngology for allergic rhinitis.

How is egg allergy diagnosed?

Diagnosis is primarily based on a detailed medical history, combined with skin prick tests or serum food-specific IgE (sIgE) test results ^[2,11-13].

1. Medical history inquiry.

The patient is asked whether they have a history of consuming eggs and whether clinical symptoms recur each time eggs are eaten.

2. Skin and serum tests.

• If the skin prick test is positive and accompanied by relevant clinical symptoms, and the serum food-specific IgE (sIgE) test is positive, the positive predictive value for diagnosing egg allergy exceeds 95%;
• If both test results are negative, the likelihood of egg allergy is 0;
• If one test result is positive and the other is negative, the likelihood of egg allergy is 2/3.

TREATMENT

Can egg allergy heal on its own?

No, but symptoms may gradually improve with age ^[14].

Egg allergy is related to the development of gastrointestinal mucosa. As children grow older, their digestive systems mature, and the intestinal mucosa becomes more developed, leading to symptom relief (as shown in Table 1):
Table 1 Natural resolution rates of egg allergy

Can egg allergy be completely cured without recurrence?

Egg allergy cannot be completely cured.

Egg allergy is an immune response, and the only way to prevent reactions is to avoid consuming eggs.

What are the treatment methods for egg allergy?

The main treatments include dietary avoidance, medication, and immunotherapy ^[15,16].

• Dietary avoidance: Avoiding eggs is the only effective way to prevent allergic reactions.
• Medication: Antihistamines, epinephrine, corticosteroids, and other hormonal drugs ^[14] are primary treatments for non-severe food allergies.
• Immunotherapy: Patients can undergo oral immunotherapy (OIT) by consuming small, controlled amounts of egg protein to build tolerance. This helps reduce severe reactions upon accidental exposure.

DIET & LIFESTYLE

What should people with egg allergies pay attention to in daily life?

• Be cautious when consuming eggs and egg products (such as cakes, egg tarts, etc.);
• Avoid certain vaccines produced in chicken embryo culture media, such as MMR (measles, mumps, rubella) and flu vaccines, as they may also trigger severe allergic reactions ^[2];
• For breastfeeding infants showing egg allergy symptoms, mothers are advised to avoid eating eggs to help reduce the baby's allergic reactions;
• If an egg allergy occurs, seek immediate medical treatment for symptomatic relief;
• Maintain a regular daily routine and engage in physical exercise.

PREVENTION

How to prevent egg allergy?

The only way to prevent it is to avoid foods containing allergens (i.e., eggs).

• When purchasing food, pay attention to allergen labels or ingredient lists to avoid buying foods or egg products containing eggs.
• If you are unsure whether a food contains eggs or is made from eggs, you can heat it before consumption. Raw foods are more likely to cause allergies than cooked foods, and heating can deactivate most food antigens that trigger allergies.