Do you have Food Allergies? Millions of people do. Allergies of all kinds are very common. What are Food Allergies? Food allergy is an immune system reaction that occurs soon after eating a certain food. Even a tiny amount of allergy-causing food can trigger signs and symptoms such as digestive problems, hives, or swollen airways. In some people, a food allergy can cause severe symptoms or even a life-threatening reaction that is known as anaphylaxis. Get tested now and find out what foods you should not be eating.