Eggs can be a great source of protein as a part of a healthy diet. But you can be allergic to some of the proteins that are found in either the egg yolk or the egg white, or even both. An egg allergy, like any allergy, is when your immune system identifies these proteins as harmful. When you ingest these proteins, your immune system becomes sensitized and overreacts, and releases histamines, which then cause your allergic symptoms. People with an egg allergy must avoid both the egg white and the egg yolk because it’s not possible to completely separate the egg white from the yolk.