A small minority of adults – less than five percent – have true allergies to foods. Common food allergens include milk, eggs, peanuts, tree nuts, shellfish, soy and wheat. When true food allergies occur, the immune system reacts to a benign substance as if it were a harmful one, and produces antibodies against it, releasing histamines and other compounds in the process. This causes symptoms such as a tingling mouth, hives, swollen tongue and throat, drop in blood pressure, or even anaphylactic shock.
Food intolerance - which is much more common - may produce less serious but still uncomfortable symptoms (diarrhea, gas, headaches or flushing). Food intolerance may be due in part to a lack of enzymes needed to break down food.
If you feel you have a true food allergy, or have been bothered by symptoms of food intolerance, talk with your physician about your concerns; he or she can arrange tests to determine what, if anything, is causing allergies or intolerance.
My thoughts on allergy testing: blood vs. skin tests