Egg allergy is an immune hypersensitivity to proteins found in chicken eggs, and possibly goose, duck, or turkey eggs. Symptoms can be either rapid or gradual in onset. The latter can take hours to days to appear. The former may include anaphylaxis, a potentially life-threatening condition which requires treatment with epinephrine. Other presentations may include atopic dermatitis or inflammation of the esophagus.

In the United States, 90% of allergic responses to foods are caused by cow's milk, eggs, wheat, shellfish, peanuts, tree nuts, fish, soybeans, and sesame seeds. The declaration of the presence of trace amounts of allergens in foods is not mandatory in any country, except for Brazil.

Prevention is by avoiding eating eggs and foods that may contain eggs, such as cake or cookies. It is unclear if the early introduction of the eggs to the diet of babies aged 4–6 months decreases the risk of egg allergies.

Egg allergy appears mainly in children but can persist into adulthood. In the United States, it is the second most common food allergy in children after cow's milk. Most children outgrow egg allergy by the age of five, but some people remain allergic for a lifetime. In North America and Western Europe, egg allergy occurs in 0.5% to 2.5% of children under the age of five years. The majority grow out of it by school age, but for roughly one-third, the allergy persists into adulthood. Strong predictors for adult-persistence are anaphylaxis, high egg-specific serum immunoglobulin E (IgE), robust response to the skin prick test, and absence of tolerance to egg-containing baked foods.

Food allergies usually have an onset from minutes to one to two hours. Symptoms may include: rash, hives, itching of mouth, lips, tongue, throat, eyes, skin, or other areas, swelling of lips, tongue, eyelids, or the whole face, difficulty swallowing, runny or congested nose, hoarse voice, wheezing, shortness of breath, diarrhea, abdominal pain, lightheadedness, fainting, nausea, or vomiting. Symptoms of allergies vary from person to person and may vary from incident to incident. Serious danger regarding allergies can begin when the respiratory tract or blood circulation is affected. Wheezing, a blocked airway, and cyanosis can indicate the former, whereas a weak pulse, pale skin, and fainting can indicate the latter. When these symptoms occur, the allergic reaction is called anaphylaxis. Anaphylaxis occurs when IgE antibodies are involved, and areas of the body that are not in direct contact with the food become affected and show severe symptoms. Untreated, this can proceed to vasodilation and a low blood pressure situation called anaphylactic shock.

Young children may exhibit dermatitis/eczema on the face, scalp, and other parts of the body; in older children, knees and elbows are more commonly affected. Children with dermatitis are at a greater than expected risk of also exhibiting asthma and allergic rhinitis.

The cause is typically the eating of eggs or foods that contain eggs. Briefly, the immune system overreacts to proteins found in eggs. This allergic reaction may be triggered by small amounts of egg, even egg incorporated into cooked foods, such as cake. People with an allergy to chicken eggs may also be reactive to goose, duck, or turkey eggs.

Influenza vaccines are created by injecting a live virus into fertilized chicken eggs. The viruses are harvested, killed and purified, but a residual amount of egg white protein remains. For adults ages 18 and older, there is an option to receive recombinant flu vaccines (RIV3 or RIV4), which are grown on mammalian cell cultures instead of in eggs, and so are not a risk for people with severe egg allergy. Recommendations are that people with a history of mild egg allergy should receive any IIV or RIV vaccine. People with a more severe allergic reaction may also receive any IIV or RIV, but in an inpatient or outpatient medical setting, administered by a healthcare provider. People with a known severe allergic reaction to influenza vaccine (which could be egg protein, gelatin, or the neomycin components of the vaccine) should not receive a flu vaccine.