Egg allergy

Cause

Giving eggs to babies early in life appears to decrease the risk of later allergies.

Mechanism

Most people who are allergic to hen's eggs have antibodies which react to one of four proteins in the egg white: ovomucoid, ovalbumin, ovotransferrin, and lysozyme; ovomucoid, also called Gal d 1, is the most common target of immune system attack. The egg yolk contains several potential antigens: livetin, apovitillin, and phosvitin.

A person who reacts only to a protein in the egg yolk may be able to easily tolerate egg whites, and vice versa. Some people will be allergic to proteins in both the egg white and the egg yolk. Egg yolk allergies may be somewhat more common in adults. A small number of people who are allergic to eggs will develop an allergy to chicken or other poultry meats.

Egg white intolerance

Egg whites, which are potent histamine liberators, also provoke a nonallergic response in some people. In this situation, proteins in egg white directly trigger the release of histamine from mast cells on contact. Because this mechanism is classified as a pharmacological reaction, or "pseudoallergy", the condition is considered a food intolerance instead of a true IgE-based allergic reaction.

The response is usually localized, typically in the gastrointestinal tract. Symptoms may include abdominal pain, diarrhea, or any symptoms of histamine release. If sufficiently strong, it can result in an anaphylactoid reaction, which is clinically indistinguishable from true anaphylaxis.

Some people with this condition tolerate small quantities of egg whites. They are more often able to tolerate well-cooked eggs, such as found in cake or dried egg-based pasta, than loosely cooked eggs, such as fried eggs or meringues, or uncooked eggs.

Diagnosis

Diagnosis is generally made through a combination of skin prick testing or blood testing and detailed records of all foods and drink the person regularly ingests.

Treatment

There is currently no cure for egg allergy. Most people who are allergic to eggs avoid eating any form of egg or egg component. For people with more serious allergic reactions to eggs, such as urticaria (hives), inflammation, and/or anaphylaxis, doctors suggest carrying an EpiPen for use in emergency. Certain food companies also produce egg substitutes, artificial brands of egg mix or batter, which have the same cooking properties of natural eggs but are free of allergens, allowing safe consumption by those whom are allergic.

Cooking without eggs

In cooking, eggs are multifunctional: they may act as an emulsifier to reduce oil/water separation (mayonnaise), a binder (water binding and particle adhesion, as in meatloaf), or an aerator (cakes, especially angel food). Some commercial egg replacers can substitute for particular functions (potato starch and tapioca for water binding, whey protein for aeration or particle binding, or soy lecithin for emulsification). For use on the skin, one-half cup of applesauce can replace one egg in some baking recipes.

Most people find it necessary to strictly avoid any item containing eggs, including:

Ingredients that sometimes include egg are:

Prognosis

In a study presented at the 2007 American Academy of Allergy, Asthma, and Immunology (AAAAI) meeting, 50% of people outgrew egg allergy by age 17. Of those patients who outgrew it, 45% did so by age 5. Children who outgrew the allergy tended to have peak IgE levels at around age one, which then decline.

Vaccine hazard

The flu vaccine is typically made using chicken embryo, and as a result the final vaccine does contain egg proteins. Egg-allergic individuals may react to egg protein(s) in the vaccine (or to gelatin or neomycin if they are allergic to that). If an individual is unable to take the vaccine, vaccinating all other members of their family can help protect them from the flu (see Herd immunity).

Different brands and even individual batches of flu vaccine do vary in their egg protein content. Allergists formerly used skin testing with flu vaccine to predict if receiving the flu shot might be safe, but the results of this type of testing are totally unpredictive and this type of testing should be abandoned. Instead, the age-appropriate immunization material containing the lowest amount of egg proteins should be chosen, then a 1/10 dose should be given followed by a 30-minute observation period in a medical setting fully equipped to treat any possible reaction. Ovalbumin is usually used as a marker for the egg proteins. Vaccines available as recently as 2010 in the US contained up to 21 µg of ovalbumin per 0.5 mL dose. In 2011 the ovalbumin content varies from less than 5.0 µg/dose down to less than 0.05 µg/dose, depending on the brand. One study done on 83 egg allergic patients resulted in a lack of serious reactions at doses of ovalbumin ranging from 0.10 µg to 0.60 µg. Thus so some brands available in the US in 2011 are probably safe for most egg allergic patients (administered with caution), but others may not be. For reference modern MMR vaccine (which is generally accepted now to be well tolerated by egg allergic patients, but which is still given with caution) was shown in a 2009 study reported in the BMJ to contain 0.0005 to 0.0010 µg/dose (0.5 to 1.0 ng/dose).

Egg proteins can also be found in yellow fever vaccine and MMR vaccine. The quantity of egg protein in a dose of MMR vaccine is approximately 40 picograms (much lower than in influenza vaccine, which contains approximately 0.02-1.0 micrograms), and this is believed to be associated with a much lower risk.

Notable cases

Famous people allergic to eggs include: