Often, patients come in telling us what foods they are allergic to on the basis of allergy testing done years before. It's quite possible that they are not allergic to those foods at all. Allergy testing is very accurate when we test for dust mites, mold, and pollen. But it's less accurate when we test for foods. Years ago, many allergists, even those board certified by the American Board of Allergy and Immunology, would tell patients to avoid foods on the basis of skin test results alone. The most reliable way to confirm a food allergy is with a food challenge. This test involves giving a capsule to a patient that contains either the food that they suspect or a placebo. To ensure the objectivity and validity, the patient (and often the doctor) doesn't know which capsule they receive.
Reactions can range from immediate itching or swelling of the lips and/or tongue, to hives, coughing, and wheezing. These usually happen within a few minutes after eating the food, sometimes up to an hour. But some true food allergies cause stomach cramping and diarrhea hours later. Unfortunately, there are no safe and effective forms of allergy shots or allergy drops for food allergy at this time. Food allergies can be life-threatening, especially if one is allergic to peanuts, shellfish, or tree nuts. Besides avoiding these foods, the doctor should prescribe an injector device with epinephrine (adrenaline) to be available at all times. Make sure that the one you buy has at least 12 months left until it expires. You often get the freshest at 24-hour pharmacies. Still, if anaphylaxis occurs and all you have is an expired device, good research shows that it's still worthwhile using it.
A careful distinction must be made between "food allergy" and "food intolerance." Many people have lactose intolerance, which causes gastrointestinal symptoms upon eating milk products. Other examples of food intolerance include headaches from drinking wine or a runny nose from eating spicy foods.