Egg allergy

Egg allergy is one of the most common food allergies in childhood accounting for 0.5%–2.5% of allergies in children ¹⁾. An Australian study reported that the prevalence of IgE-mediated egg allergy in infants aged 12 months is 9 percent ²⁾. Egg is also the most important cause of food allergy among single foods in Korea ³⁾. In 1995, based on the Food Allergen Cause Report, 22.7% of children with food allergy had egg allergy ⁴⁾. A recent questionnaire survey on children aged 0 to 6 years was conducted in 2014, and 20% of children with food allergy complained of egg allergy ⁵⁾. 80 percent of these infants are likely to outgrow their egg allergy within the first few years of life. Most children, even those who have had severe reactions, do eventually outgrow their egg allergy although some may not outgrow it until their teen years. A very small number of adults have egg allergy for life.

Your body’s immune system, which normally fights infections, overreacts to proteins in egg. If the person drinks or eats a product that contains egg, the body thinks these proteins are harmful invaders. The immune system responds by working very hard to fight off the invader. This causes an allergic reaction.

Egg allergy is a hypersensitivity to dietary substances from the egg yolk or egg whites, causing an overreaction of the immune system which may lead to severe physical symptoms for millions of people around the world. Egg allergy appears mainly, but not exclusively, in children. In fact, egg allergy is the second most common food allergy in children in the United States ⁶⁾. The most common is cows’ milk allergy. It is usually treated with an exclusion diet and vigilant avoidance of foods that may be contaminated with egg. The most severe food allergy reaction is called anaphylaxis and is an emergency situation requiring immediate attention and treatment with epinephrine. The Asthma and Allergy Foundation of America estimates that most children outgrow egg allergy by the age of five, but some people remain allergic for a lifetime.

Eggs are one of the most common food allergens. People with an allergy to chicken eggs may also be allergic to other types of eggs, such as goose, duck, turkey or quail. Within a short period of time after eating (or even touching) eggs, you may experience the following symptoms:

• Skin reactions, such as swelling, a rash, hives or eczema
• Wheezing or difficulty breathing
• Runny nose and sneezing
• Red or watery eyes
• Stomach pain, nausea, vomiting or diarrhea
• Anaphylaxis (less common).

If you or your child experiences any of these symptoms, see an allergist.

If your doctor suspects you might have a egg allergy, he or she will probably refer you to an allergist or allergy specialist for more testing. The allergy specialist will ask you questions — like how often you have the reaction, the time it takes between eating a particular food and the start of the symptoms, and whether any family members have allergies or conditions like eczema and asthma.

The allergy specialist may do a skin test on you. This involves placing liquid extracts of egg protein on your forearm or back, pricking the skin a tiny bit, and waiting to see if a reddish, raised spot forms, indicating an allergic reaction.

You may need to stop taking anti-allergy medications (such as over-the-counter antihistamines) or prescription medicine 5 to 7 days before the skin test because they can affect the results. Most cold medicines and some antidepressants also may affect skin testing. Check with the allergist’s office if you are unsure about what medications need to be stopped and for how long.

The doctor also might take a blood sample and send it to a lab, where it will be mixed with some of the suspected allergen and checked for immunoglobulin E (IgE) antibodies.

These types of tests are used for diagnosing what doctors call a fast-onset type of egg allergy. But for people whose allergic reactions to egg develop more slowly, skin and blood tests are not as helpful.

In these cases, doctors try to diagnose the person using a food challenge. The person is told not to eat or drink anything made with egg for a period of time — usually a few weeks. Then, during the challenge, the person eats foods containing egg under a doctor’s close supervision. If symptoms come back after eating egg products, it’s a pretty sure bet the person has a egg allergy.

To treat a egg allergy, the person who is allergic needs to completely avoid any foods that contain egg or egg products. Avoiding egg and egg products is the primary treatment for egg allergy.

Fortunately, most children outgrow egg allergy. Those who don’t outgrow it may need to continue to avoid egg products.

If you have a egg allergy, keep an epinephrine auto-injector (such as an EpiPen®, Auvi-Q™ or Adrenaclick®) with you at all times. Epinephrine is the first-line treatment for anaphylaxis. Keeping epinephrine with you at all times should be just part of your action plan for living with a egg allergy. It’s also a good idea to carry an over-the-counter antihistamine, which can help ease allergy symptoms in some people. But antihistamines should be used in addition to the epinephrine, not as a replacement for the shot.

If you accidentally eat something with egg in it and start having serious allergic symptoms — like swelling inside your mouth, chest pain, or difficulty breathing — give yourself the shot right away to counteract the reaction while you’re waiting for medical help. Always call for emergency help when using epinephrine. You should make sure your school and even good friends’ houses keep injectable epinephrine on hand, too.

If you’ve had to take an epinephrine shot because of an allergic reaction, go immediately to a medical facility or hospital emergency room so they can give you additional treatment if you need it. Sometimes, anaphylactic reactions are followed by a second wave of symptoms a few hours later. So you might need to be watched in a clinic or hospital for 4 to 8 hours following the reaction.

Figure 1. Egg allergy rash

Egg allergy and the flu vaccine

Egg-based components comprise some formulations of the influenza vaccination. Some parents are concerned about the potential of anaphylaxis should their child receive the influenza vaccination. Per 2018 American Academy of Pediatrics guidelines ⁷⁾, children with any severity of egg allergy can safely receive the influenza vaccination without additional precautions other than standard precautions that apply to any vaccination administered to any patient (egg allergy or no egg allergy). Numerous studies have confirmed the safety of influenza vaccination in patients with egg allergies ⁸⁾.

When is the best time to introduce egg into an infant’s diet?

The ideal age to introduce egg into an infant’s diet has been debated for the past two decades as egg allergy is one of the most common food allergies affecting young children. The Starting Time of Egg Protein (STEP) trial was designed to find out if egg allergy in infancy can be prevented by infants regularly eating egg from four to six months of age.

In a recent article published in The Journal of Allergy and Clinical Immunology, Palmer and colleagues ⁹⁾ studied 820 infants without eczema at study entry but all infants had a family history of allergy (atopic mothers). Each infant in this STEP trial was randomly assigned to one of two groups. One group (egg introduction) of 407 infants were introduced to egg containing powder from 4-6 months of age which was mixed into their solid foods daily. The other group (egg avoidance) of 413 infants were introduced to a colour-matched rice based (egg-free) powder also from 4-6 months of age. All families were asked to follow an egg-free diet for their infant until 10 months of age. Cooked egg was introduced to both groups of infants from 10 months of age when the study powder use was ceased. At 12 months of age, the infants had a medically observed pasteurized raw egg challenge to determine which infants had developed an egg allergy.

The authors found that feeding egg to infants between 4-6 and 10 months of age had no substantial effect on egg allergy in the first year ¹⁰⁾. Overall, 7% of infants in the group that were given the egg powder developed an egg allergy by 12 months of age compared with 10% of the infants given the egg-free powder. Whether the infants were breastfeeding had no effect on the results. Likewise feeding egg from 4-6 months of age did not affect whether the infants became sensitised to peanuts or other allergens, developed eczema or had a wheeze.

In summary, for infants without eczema symptoms, regular egg eaten in solid foods from 4-6 months of age does not substantially alter the risk of egg allergy by 1 year of age.

Egg allergy causes

Egg allergy is immunoglobulin E (IgE)-mediated and healthy individuals are capable of generating antigen-specific IgE upon exposure to egg allergens ¹¹⁾. Egg allergy is IgE mediated, and so it is classified (like all food allergies) as a type 1 hypersensitivity reaction. It is believed that there may be a genetic component to the development of egg allergy as the progeny of atopic individuals are more likely to suffer from allergies themselves. The consensus is that IgE responses are genetically controlled by major histocompatibility complex (MHC)-linked genes that are found on chromosome six. Other components that may be associated with atopy and allergy include the IgE Fc receptor located on chromosome eleven.

The major components of the immune system involved with egg allergy are mast cells and basophils. These cells are types of polymorphonuclear leukocytes (PMN), a group which also consists of eosinophils and neutrophils. The traditional view considered basophils and mast cells as the same type of cell due to their functionality and histological appearance. The major distinction between the two types of cells are the respective locations of each type of cell (basophils are serum-based while mast cells are located in the connective tissues). Despite their similarity in function and histological appearance, it is now thought that basophils and mast cells are different cells due to their distinct hematopoietic lineages.

Mast cells and basophils possess granules that contain a variety of compounds that facilitate local inflammatory response. These compounds include heparin, histamine, leukotrienes (C4, D4, and E4), and chemotactic factors. The histamine and leukotriene release causes smooth muscle contraction while histamine additional promotes increased vascular permeability. The chemotactic factors are primarily eosinophilic and neutrophilic.

Egg allergy pathophysiology

An allergic response is typically mediated by the presence of immunoglobulin E (IgE) and the process of binding of IgE to human mast cells and basophils is termed sensitization. The IgE-immune cell binding is via the fragment crystallizable (Fc) region of the IgE immunoglobulin (Fc-epsilon-RI), composed of an alpha chain, a beta chain, and two gamma chains. The process of sensitization prepares mast cells and basophils cells for antigen-specific activation. In the activation phase, reexposure to egg protein allergens initiates degranulation of mast cells and basophils with subsequent release of pharmacoactive mediators. As addressed earlier, these mediators include heparin, histamine, leukocyte chemotactic factors, and leukotrienes; these mediators are responsible for the clinical manifestations of egg allergy. The degranulation process is not apoptotic; on the contrary, degranulated mast cells or basophils regenerate and are able to resume their normal cellular function once their granular contents are synthesized. In the case of egg allergy, the cross-linking of egg protein-specific IgE on mast cells in response to egg allergen occurs in mast cells in the upper and lower gastrointestinal tract. The release of chemical mediators causes smooth muscle contraction and vasodilation, leading to emesis and diarrhea. The egg protein allergens can also be absorbed into the bloodstream due to increased vascular permeability due to histamine release. The egg proteins can interact with skin mast cells, causing atopic urticaria.

IgE is the immunoglobulin responsible for egg allergy, and the IgE responses have a TH2 dependency. While TH2-derived cytokines promote IgE response, it is balanced by TH1-derived cytokine downregulation of IgE. Egg allergy can result from a failure of this balance, leading to an overproduction of IL-4 by TH2 cells.

A majority of the immunogenic proteins are found in the egg white with five major allergenic components of egg white: ovomucoid (Gal d 1), ovalbumin (Gal d 2), ovotransferrin (Gal d 3), egg white lysozyme (Gal d 4), and ovomucin ¹²⁾. Although these are the major allergenic proteins, lipocalin-type prostaglandin D synthase and egg white cystatin have also been associated with IgE reactivity. Hen egg yolk also contains allergens, the major allergen being alpha-livetin (Gal d 5). Although Gal d 2 ovalbumin is the most abundant protein in egg white, Gal d 1 ovomucoid is the considered the dominant allergen in hen egg white.Egg specific IgE molecules can be classified as either sequential epitopes or conformational epitopes, the primary difference being the spatial relation between amino acids. Sequential epitopes have contiguous amino acid sequences while conformational epitopes contain amino acids in different regions of the protein structure. Individuals with egg allergies can tolerate cooked products containing eggs, suggesting that the allergic response is dependent on epitope configuration. Heat-labile allergenic proteins alter their arrangement with the cooking process, thus blunting or minimizing their immunogenic potential. In particular, ovalbumin proteins are heat-labile while ovomucoid epitopes are generally not affected by extensive heating.

Egg allergy symptoms

Egg allergy often presents in infancy and most symptoms are typically cutaneous in nature, often presenting with diffuse urticaria and angioedema. However, gastrointestinal symptoms such as vomiting, and/or respiratory symptoms can also occur. Symptoms often present within minutes post-exposure but can sometimes be delayed to 2 hours after ingestion. In severe cases, life-threatening anaphylaxis can occur with hen egg exposure, often requiring epinephrine administration.

When someone with an egg allergy has something with egg in it, the body releases chemicals like histamine . The release of these chemicals can cause someone to have symptoms like:

• wheezing
• trouble breathing
• coughing
• hoarseness
• throat tightness
• belly pain
• vomiting
• diarrhea
• itchy, watery, or swollen eyes
• hives
• red spots
• swelling
• a drop in blood pressure, causing lightheadedness or loss of consciousness (passing out)

Allergic reactions to egg can vary. Sometimes the same person can react differently at different times. Some reactions to egg are mild and involve only one part of the body, like hives on the skin. But even when someone has had only a mild reaction in the past, the next reaction can be severe.

Egg allergies can cause a severe reaction called anaphylaxis. Anaphylaxis can begin with some of the same symptoms as a less severe reaction, but can quickly get worse. The person may have trouble breathing or pass out. More than one part of the body might be involved. If it isn’t treated, anaphylaxis can be life-threatening.

Egg allergy can also present with two related disorders: eosinophilic esophagitis and food protein-induced enterocolitis syndrome (FPIES). Eosinophilic esophagitis is an inflammatory disorder associated with the accumulation of intraepithelial eosinophils, and it is mediated by both IgE and non-IgE processes. Egg protein is one of the more common triggering factors for the development of eosinophilic esophagitis ¹³⁾. As with other forms of esophagitis, eosinophilic esophagitis can present with dysphagia and nonspecific symptoms such as chest discomfort.

food protein-induced enterocolitis syndrome is also an inflammatory disorder characterized by vomiting, lethargy, and diarrhea. Typically symptomatic presentation in food protein-induced enterocolitis syndrome occurs 2 – 6 hours after ingestion of egg protein.

As previously mentioned, dermatitis can be a presenting symptom of an allergic reaction to egg protein exposure. This finding, however, is typically found in children less than one year of age. Atopic dermatitis onset after one year of age is not usually associated with egg allergy, and any workup should include other differentials beyond egg allergy.

Asthma has often been associated with food allergies due to the association with IgE mediated reactions. A small cohort study involving 1218 children indicated an incidence of asthma in 80% of the children with egg allergy with a calculated odds ratio of 5.0 ¹⁴⁾.

Egg allergy complications

An allergic response to egg allergens can range from dermatological manifestation (i.e. rashes, hives), gastrointestinal symptoms (i.e., diarrhea, nausea, vomiting) to potentially life-threatening anaphylaxis.

Egg allergy diagnosis

Any evaluation of suspected egg allergy should always begin with a detailed history and physical examination. History should include dietary intake of an egg (amount, frequency per day, form.), reactions (i.e., diarrhea, rash, etc.) and the time of onset of symptoms after ingestion of egg or egg-containing product. Family history may also provide important clues, especially if there is documented or suspected egg allergy in a parent or sibling.

An egg allergy is diagnosed with skin tests or blood tests. A skin test also called a scratch test is the most common allergy test. Skin testing lets a doctor see in about 15 minutes if someone is sensitive to egg.

With skin test, the doctor or nurse:

• puts a tiny bit of egg extract on the skin
• pricks the outer layer of skin or makes a small scratch on the skin

If the area swells up and get red (like a mosquito bite), the person is sensitive to eggs.

A blood test can be used if a skin test can’t be done. It takes a few days/weeks to get the results of blood tests, though, and these tests are not perfect. It’s important to be checked by a health care provider who has experience with allergy testing.

Egg allergy test

Diagnostic evaluation for suspected hen egg allergy includes skin testing (in which small quantities of allergenic egg proteins are introduced subcutaneously and monitored for reaction), egg-specific serum IgE levels, and oral food challenges. Although food diaries (a written log of everything the patient consumes) are non-diagnostic, they can be useful in identifying egg as a potential allergen. Among the diagnostics evaluations for egg allergy, the double-blinded, placebo-controlled oral food challenge is considered the gold standard for assessment and diagnosis of suspected egg allergy. Unlike egg-specific serum IgE levels, the oral food challenge should be done under the close supervision of a trained professional for the significant possibility of anaphylaxis.

Skin testing involves the introduction of an allergen into the subcutaneous tissue. The allergen introduction prompts the cross-linking of antigen-specific IgE to mast cells, resulting in degranulation and subsequent urticaria. The food allergens are applied with respective positive (histamine) and negative (saline) controls. Upon introduction of the egg allergen to the skin, a reaction is observed. Mast cell degranulation occurs in the presence of egg protein IgE antibody, leading to the release of histamine. It is generally accepted that a weal of 3 mm or greater in diameter is considered a positive result. Skin testing, however, can have a higher rate of false negatives, mainly if the patient used antihistamines or Benadryl within a week before skin allergen testing. Also, skin testing should not be performed for several weeks after an episode of anaphylaxis since anaphylaxis can lead to a temporary nonreactivity of the skin, thus increasing the false-negative rates.

Immunoassay diagnostics include radioallergosorbent tests (RASTs) and fluorescent enzyme immunoassay (FEIA). They are less sensitive than skin testing but are not affected by prior antihistamine use. If there is a concern for significant anaphylaxis, immunoassays can be used safely. Test results for egg allergen serum IgE levels are measured in kUA/L units and provide important predictive levels of experiencing an allergic response to an oral food challenge. According to [6], an egg allergen IgE levels seven kUA/L (or 2 kUA/L if children are less than two years of age) is associated with a 95 percent predictive value. The clinical interpretation is as follows: A patient (greater than two years of age) with a concerning history of egg allergy has 95% likelihood of experiencing an allergic reaction to egg upon challenge if their egg-specific IgE levels exceed 7 kUA/L. If a patient’s egg-specific IgE serum level exceeds this threshold, an oral food challenge may not be warranted.

Oral food challenges (especially double-blinded, placebo-controlled) are the gold standard for the diagnosis of egg allergy. The utility of an oral food challenge depends on several factors. If an egg is not a component of a patient’s daily diet and can just be avoided, an oral food challenge may not be warranted. In addition, if the patient has a clinical history suspicious of egg allergy coupled with elevated egg-specific IgE serum levels, the oral food challenge may be deemed unnecessary.

Open oral food challenges involve the gradual oral introduction of an egg to a patient. Both the patient and observer are both aware of that egg is being introduced, leading to increased susceptibility to bias (especially if symptoms present). The open oral food challenge, however, is easy to perform as it requires no special preparation. Single-blinded oral food challenges involve the oral introduction of egg in a vehicle (I.e., in another food source in opaque capsules) to blind the patient to what intervention is performed. It eliminates patient bias but is still prone to observer bias.

Oral food challenges require adequate preparation for accurate results. All antihistamines, beta-agonists, and beta-blockers (including eye drops) should be discontinued for a specified amount of time before an oral food challenge. The oral food challenge should be done under the clinical supervision of a trained physician trained in treating anaphylaxis should it occur.

Egg allergy differential diagnosis

Egg allergy presents with non-specific symptoms and can often be confused for general food intolerance, gastrointestinal upset, or another associated food allergy.If a patient is lactose intolerant and consumes a milk product that can contain egg product (i.e., custard, ice cream), the gastrointestinal symptoms can be falsely attributed to egg allergy although there is no exact IgE-mediated allergic reaction. Skin manifestations (such as atopic dermatitis) can be due to contact allergies.

Egg allergy treatment

Due to risks of life-threatening anaphylaxis, any suspected egg allergy should be managed initially with complete avoidance of egg exposure with appropriate follow up with an allergist. Oral food challenges should not be attempted unless supervised by a trained clinician.

Avoidance of egg exposure is the most effective form of egg allergy management but is not equivalent to cure and may not always be feasible. Unfortunately, efforts of avoiding exposure can pose a significant psychosocial stressor on both the child and the parents. Instead of being engaged in their child’s day-to-day routine, parents may find themselves more focused on scrutinizing any potential exposures. “Egg-free” food items may be more expensive compared to their egg-containing counterparts. Children, wanting to socialize with their peers, may feel more isolated and withdrawn. Also, avoidance of eggs (or any food allergen) can place children at higher risk for nutritional deficiencies ¹⁵⁾. For instance, in a study comprised of two hundred and forty two children (mean age of four) ¹⁶⁾ in which subjects were to abstain from particular food items completely, the participants less than two years of age with the dietary restriction had lower body mass index profiles compared to their control counterparts of similar age. Oral immunotherapy involves oral administration of allergenic egg white with an edible vehicle in gradually increasing dosages. Oral immunotherapy has demonstrated the success of desensitization in patients with egg allergy ¹⁷⁾. However, it remains relatively time-consuming and often requires long term maintenance therapy.

Avoiding egg and egg products

If you have an egg allergy, avoid eating egg. Read food labels carefully, because ingredients can change and egg can be found in unexpected places.

Some foods look OK from the ingredient list, but while being made they can come in contact with egg. This is called cross-contamination. Look for advisory statements such as “may contain egg,” “processed in a facility that also processes egg,” or “manufactured on equipment also used for egg.” Not all companies label for cross-contamination, so if in doubt, call or email the company to be sure.

You and anyone else preparing your food should wash hands well with soap and water before touching it. Always wash your hands before eating. If you don’t have soap and water, you can use hand-cleaning wipes. But don’t use hand sanitizer gels or sprays. Hand sanitizers only get rid of germs — they don’t get rid of egg proteins.

At home, keep foods that contain egg in a separate part of your kitchen so they don’t contaminate your food. When preparing food, wash dishes and utensils with dishwashing soap and hot water to remove any traces of egg.

When eating away from home, keep your epinephrine auto-injector with you and make sure that it hasn’t expired. Also, tell the people preparing or serving your food about the egg allergy. Sometimes, you may want to bring food with you that you know is safe. Don’t eat at the restaurant if the chef, manager, or owner seems uncomfortable with your request for a safe meal.

Ingredients to avoid if you are allergic to egg*:

• Albumin
• Apovitelin
• Avidin
• Binder
• Dried eggs
• Egg
• Egg solids
• Egg substitutes (some)
• Egg white
• Egg white solids
• Egg yolk
• Flavoproteins
• Glaze (on baked goods)
• Globulin
• Imitation egg product
• Livetin
• Lysozyme
• Meringue mix
• Ovalbumin
• Ovglycoprotein
• Ovomucoid
• Ovovitelin
• Powdered egg
• Silica albuminate
• Simplesse

Note: *This is not a complete or comprehensive list of ingredients to avoid but is intended as a helpful aid for living with egg allergy. It is NOT meant to replace medical advice given by your doctor.

Products which might contain egg include:

• Baked products
• Battered foods
• Biscuits
• Cakes (eg sponge, angel)
• Confectionary
• Crumbed foods
• Custards
• Doughnuts (donuts)
• Drink mixes
• French toast
• Frittatas
• Fritters
• Frozen desserts
• Glazed foods
• Icing on cakes
• Macaroons
• Malted drinks
• Marshmallow
• Marzipan
• Mayonnaise
• Meat loaf/hamburgers
• Meringue
• Mousse
• Naan bread
• Noodles
• Nougat
• Omelettes
• Pancakes, pikelets
• Pasta
• Pastries
• (eclairs, creampuffs, tarts)
• Pavlovas
• Pizzas
• Quiche
• Quick breads
• Rissoles
• Salad dressings
• Sauces (eg Hollandaise)
• Soufflés
• Soups
• Sushi
• Sweets/lollies
• Vegetarian meat substitutes (eg vegetarian sausages)
• Waffles

Remember: Cosmetics, lotions, shampoos, moisturizers and the like can contain food allergens. Some medications (prescribed and over the counter) and alternate therapies can also contain food allergens.

Egg allergy prognosis

A significant majority of patients with hen egg allergy will develop tolerance to egg allergens by the time they reach school age. Egg allergy resolved in half of the children at the median age of 6 years; however, a wide range from 2 to 9 years has been reported for the age at resolution. However, some build tolerance only in adolescence. The review by Savage et al. ¹⁸⁾ revealed that the differences in resolution rates and ages in each study were due to the different study designs, and definitions of egg allergy and development of tolerance. The resolution rate most likely depended on the definition of development of tolerance including the method of food challenge test ¹⁹⁾. In this study ²⁰⁾, 81.5% of children developed tolerance to egg by the median age of 3 years. The resolution rate was much higher compared to the previous study, a retrospective study in a tertiary referral clinic with similar criteria of egg allergy and development of tolerance, which reported that only 19% of children acquired tolerance to egg allergy by age 4 years ²¹⁾. Forty percent of Korean children with atopic dermatitis ²²⁾ and 30% of Japanese children ²³⁾ had tolerance to egg by the age of 3 years. These Asian studies reported favorable resolution rates of 70% by the age of 6 years and 85% by the age of 10 years compared to the previous Western studies ²⁴⁾. The differences may be due not only to different populations but also different lifestyles including dietary habits.

Prognostic factors for the development of tolerance include baseline levels of egg-specific IgE, early age of diagnosis, the severity of symptoms, skin test weal size on skin prick testing, and tolerance of extensively heated egg. Egg specific serum IgE to IgG4 ratios may be useful for predicting tolerance ²⁵⁾ although it is not routinely used. Larger skin prick test wheal size ²⁶⁾ or high egg-specific IgE levels ²⁷⁾ were associated with persistent egg allergy. Regarding weal size, a 2013 cohort study demonstrated that a weal size of approximately 5 mm correlated to a 95% positive predictive value for egg allergy ²⁸⁾. The meta-analysis that evaluated this study indicated the benefits of performing skin allergen testing before an oral food challenge. Although relatively nonspecific, weal size correlation with positive predictive value could prevent children from undergoing more time consuming oral food challenges.

Persistence of egg allergy has been associated with more severe symptoms ²⁹⁾, the presence of other allergic diseases and their severity ³⁰⁾. The clinical characteristics associated with the natural history of egg allergy in this study were presence of other food allergies and atopic dermatitis. More than half of the children had other food allergies and children with comorbid peanut or wheat allergies had persistent egg allergy. Eighty percent of children had other comorbid allergic diseases and the majority was atopic dermatitis. The results of this study ³¹⁾ showed that comorbid atopic dermatitis in children with egg allergy was an indicator of poor prognosis, which is consistent with other studies, while the resolution rate in this study was much higher compared to that of previous studies that reported lower resolution rates in children with atopic dermatitis ³²⁾.

Moreover, Kim et al ³³⁾ showed that the egg white-specific immunoglobulin E levels at diagnosis (EWsIgEdiag) and the peak egg white-specific immunoglobulin E were higher in the persistent group than in the tolerant group. The egg white-specific immunoglobulin E levels at diagnosis has been suggested as a predictor of tolerance acquisition. Tolerance acquisition was reported to be significantly delayed when the baseline egg-specific IgE level was ≥ 6.2 kU/L ³⁴⁾ or ≥ 10 kU/L ³⁵⁾ and failed in almost all children when the peak egg-specific IgE level was ≥ 50 kU/L ³⁶⁾.