Egg allergy is a type of food allergy. It is a hypersensitivity to dietary substances from the yolk or whites of eggs, 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, it is the second most common food allergy in children. 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.