A food allergy is an abnormal response to a food triggered by the body's immune system. People often confuse a food allergy with a food intolerance. Healthcare providers conduct specific tests in order to make a definitive diagnosis. Possible symptoms include itching in the mouth, vomiting, hives, and asthma. In some cases, the reaction can be so severe that it causes serious illness, or even death. Treatment usually involves avoiding the food that triggers the reaction.