If you go to an allergy doctor and get a skin prick test or a blood test for food allergies, you might not like what you see. Many patients end up with a laundry list of foods they can't have because the tests show a food allergy. But doctors and patients are both starting to find that these tests often show up positive for foods that the patient is not really allergic to. And, these long lists of "forbidden foods" can lead to a lot of frustration for a person trying to avoid an allergic reaction but still eat and enjoy food.

It's not that these tests are bad or should not be used. The problem is that they should not be used alone to diagnose a food allergy but rather to help confirm other tests.

What is a food allergy? A true food allergy is an immune reaction to a specific food. In an immune response, certain cells in the body release chemicals when they come in contact with a food's protein. These chemicals then cause symptoms like hives, rashes, itching, or trouble breathing.

The way a person reacts to an allergic food can very mild to very serious. About 200 people a year die from food allergies. About 30,000 end up in the emergency room - unintentional exposure causes about half of these reactions. Children are more likely than adults to have food allergies - 6 to 8% of children compared to 3 to 4% of adults. But children are more likely to outgrow their allergies as they get older.

Food allergies are not food intolerances. If you have lactose intolerance, you are not allergic to lactose. You just can't break down the sugar in milk, lactose, and digest it. But if you are allergic to milk then you have an immune response to a protein in the milk. Food intolerances do not cause an immune response.

The Usual Suspects
Eight foods top the "most likely to offend" list - causing 90% of food allergies:

  • Eggs
  • Milk
  • Peanuts
  • Tree Nuts (like walnuts, almonds, cashews)
  • Shellfish
  • Fish
  • Soy
  • Wheat

Peanuts and tree nuts are more likely than the others to cause severe reactions. If you think you have a food allergy, your doctor should talk to you about several ways to give you an accurate diagnosis. Using several of these will give you the best diagnosis.

Top Tests for Food Allergies:
You should use these tests only under the guidance of a physician who specializes in food allergies.

  • Diet Diary: Keep a food diary and record any reactions - what they are and when they happened. Don't use the diet diary method if you have had serious reactions - like trouble breathing - from suspect foods.
  • Elimination Diet: After keeping a food diary, you stop eating the foods you think are causing the reaction and then start adding them back under a doctor's supervision. If you have a reaction when you add back the food you stopped eating, then you are probably allergic to it.  As with the diet diary, don't use this test if you suspect that your reactions are severe.
  • Skin Prick Test:  Using the skin prick test, the doctor will prick your skin with an extract of the suspected food. If there is a local reaction, you might be allergic to the food. But beware! You may test positive for foods that you're not really allergic to and up eliminating foods that you don't need to. So, this test should be used along with your medical history and, if possible, a diet diary to give you an accurate diagnosis.
  • Blood Test: The doctor will do a blood test to see what antibodies you have for foods. But just like the skin prick test, positive results don't mean that you are actually allergic to the food. So this is where a good medical history and a food diary can really help to clarify your diagnosis.

Treating a food allergy. The only way to treat a food allergy is to stop eating the offending food. It's now easier to spot foods with the big eight offenders than in the past. Since 2006, food makers must  plainly label a product if it contains one of the eight major allergy-causing foods. So label reading skills comes in very handy for consumers with food allergies.

Look on the ingredients list and you'll see wording like these two examples:

Ingredients: Enriched flour (wheat); lecithin (soy)


Contains peanuts, eggs

If you're eating out at a restaurant or at friend's house, be sure to ask questions about how the food was prepared and let the cook know about your food allergies.

For more information, visit www.foodallergy.org

Beth Kitchin, MS, RD
Assistant Professor
UAB Nutrition Sciences Department