As with other food allergies, an allergy to eggs is the result of your immune system misidentifying certain proteins. Instead of recognizing egg proteins as safe, your body flags them as dangerous invaders. It then releases an antibody called immunoglobulin E to combat the allergen. In turn, the antibody then sends out a host of chemicals to fight off the egg allergens; one of those chemicals is histamine. Histamine is responsible for many of the allergic symptoms you feel as your immune system wages the war on egg proteins.
Symptoms can set in anywhere from a few minutes to a few hours after you eat eggs. While everyone reacts differently, the most common symptoms include skin problems like swelling and hives. Other common symptoms are respiratory in nature, like asthma that's brought on by the allergy, runny nose, sneezing and watery eyes. Some people have stomach problems as a result of an egg allergy; they can end up nauseous, vomiting, with diarrhea or cramps. More rarely, people with egg allergies can experience anaphylaxis after eating egg proteins; such people require immediate medical care. If they have epinephrine on hand, that should be the first step. After that, they need to see a doctor. For the more common and less severe egg allergy symptoms, over-the-counter antihistamines can usually relieve the discomfort associated with the allergic reaction.
Keep in mind that symptoms alone aren't enough to diagnose an egg allergy. A trip to the allergist will help determine whether your allergic symptoms are related to eggs or whether they're the result of something else. The doctor will consider your family's allergy history and your personal history of symptoms. He may also perform a skin test to ascertain whether you're allergic to eggs. Some doctors do blood tests, as well.