Food allergies occur when the immune system mistakes harmless food proteins as harmful and releases chemicals to fight them. The most common allergens include peanuts, tree nuts, nuts, milk, eggs, fish, shellfish, soy and wheat. Food allergy can be hereditary, which means it can run in families. In addition, exposure to certain environmental factors, such as pollution and toxins, can also increase the risk of developing food allergy.The symptoms of food allergy can range from mild to severe and can occur within minutes to several hours after exposure to the allergen. Common symptoms include itching or swelling of the mouth, throat and face, hives or rash, vomiting or diarrhea, abdominal cramps, difficulty breathing and, in severe cases, anaphylaxis, a life-threatening reaction that can cause difficulty breathing, loss of consciousness and even death.