Food allergy is an immune system reaction that occurs soon after eating a certain food. Even a tiny amount of the allergy-causing food can trigger signs and symptoms such as digestive problems, hives or swollen airways. Food allergy affects an estimated 6 to 8 percent of children under age 3, and about 4 percent of adults. While there’s no cure, some children outgrow their food allergy as they get older. It’s easy to confuse a food allergy with a much more common reaction known as food intolerance. While bothersome, food intolerance is a less serious condition that does not involve the immune system.