Food allergies are the result of a mistake made by your immune system. Your body misinterprets certain proteins and thinks they're dangerous -- despite the fact that they're perfectly safe. When you eat foods that contain those proteins, your body reacts. Your immune system sends out an antibody called immunoglobulin E; the antibody then sends out a team of chemicals to fight off the protein, or allergen. Among those allergen-fighting chemicals is histamine. Histamine is responsible for most of your allergic symptoms in your respiratory system, gastrointestinal tract, skin or cardiovascular system.
Among these symptoms of food allergies is swelling. While it's normally your lips, tongue and throat that swell, you can swell up anywhere when you eat a food you're allergic to. Swelling as a result of a food allergy can happen any time from a few minutes to a few hours after you eat the food you're allergic to.