How Does a Doctor Diagnose an Allergy?

If you have itchy, watery eyes or a stuffy, runny nose, you could have a cold. But if you feel bad only when you're outside, are near pets, or eat certain foods, you could have an allergy.

Some people with allergies sneeze a lot or get rashes or hives that don't spread to other parts of their body. But others can have such a bad reaction that they have trouble breathing and need medical help right away.

It's good to know if you have allergies so you can stay away from the things that trigger them -- called allergens -- and get medicine if you need it.

If you think you have an allergy, you'll see a doctor who specializes in allergies called an allergist. He'll ask questions about your health and any family history of asthma or allergies. He'll also examine you and recommend a few tests to find out for sure.

Skin Tests

The most common way to test for allergies is with a skin test. That's because it gives the fastest, most accurate results.

The one doctors use most often is called a scratch test. A doctor or nurse will put a tiny drop of an allergen on your skin, usually on the inside of your arm or on your back. Common allergens include mold, pollen, pet skin and fur, foods, and some medicines.

Next, she'll prick your skin or make a small scratch on the surface to let the allergen get underneath it. The skin prick won't make you bleed. You'll feel it, but it shouldn't hurt. Some doctors use a small needle to put the allergen under the first few layers of your skin.

The doctor will probably test several things at the same time. If one of the areas swells up and gets red like a mosquito bite, it means you're allergic to that allergen. It usually takes about 15 minutes to find out.

When the test is over, the doctor or nurse will clean your skin and put some cream on it to help with any itching. Any swelling from a reaction usually goes away within 30 minutes to a few hours.

Some medicines can get in the way of the tests. Check with your doctor to see if you need to stop taking any medication before the test.

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Blood Tests

If you take medicine that could affect allergy test results, have sensitive skin, or have had a bad reaction to a skin test, your doctor might do a blood test instead.

A sample of your blood is sent to a lab, and your doctor will get the results within a few days. This is typically more expensive than a skin test.

Food Allergies

If your doctor thinks you might be allergic to a certain food or foods, she may ask you to stop eating them to see if that helps. This is called an elimination diet.

You'll cut out those foods for 2 to 4 weeks and see if you have any allergy symptoms during that time. If you don't, your doctor will ask you to start eating the foods again to see if your symptoms come back. If they do, there's a good chance you're allergic to those foods.

Your doctor also might ask you to do something called an oral food challenge. This should only be done in a medical office by an allergist.

Your doctor will give you very small amounts of the food you may be allergic to and watch for symptoms. If you don't have any, he'll slowly give you larger doses. If you start to have symptoms, he'll stop the test.

The most common signs are hives or a flushed feeling. If that happens, he'll give you medicine to make you feel better. If you don't have a reaction, you can rule out an allergy to that food.

WebMD Medical Reference Reviewed by William Blahd, MD on January 25, 2017

Sources

SOURCES:

American College of Allergy, Asthma and Immunology: "Allergy Testing," "Diagnosing Allergies."

American Academy of Family Physicians: "Colds and the Flu: Tips for Feeling Better."

Cleveland Clinic: "Allergies," "Allergy Overview," "Allergy Tests."

Food Allergy Research and Education: "Food Elimination Diet," "Oral Food Challenges."

Kidshealth.org: "Allergy Testing," "How Do Doctors Test for Allergies?" "Serious Allergic Reactions (Anaphylaxis)."

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