A food allergy happens when your immune system - your body's defense against germs - overreacts to a certain food as if it was harmful. If you have symptoms after eating certain foods, food allergy testing can help find out if your symptoms are caused by an allergic reaction to those foods. And it's important to find out because allergic reactions to food can be serious.

Most food allergy symptoms are mild and include skin rashes and abdominal (belly) pain. But sometimes, symptoms quickly develop into a life-threatening allergic reaction called anaphylaxis, or anaphylactic shock. Anaphylaxis is a medical emergency that may affect your whole body, including your breathing. And there's no way to predict when an allergic reaction may change from mild to serious.

If you have a food allergy, eating even tiny amounts of a certain food or ingredient can quickly trigger your immune system to react. Most food allergies are caused by:

• Milk
• Eggs
• Peanuts
• Tree nuts (including almonds, walnuts, pecans, and cashews)
• Soy
• Wheat
• Fish
• Shellfish

Food allergies are more common in children than adults. Most children will grow out of allergies to milk, egg, soy, and wheat. But if a food allergy begins in adulthood, it's likely to continue through life.

If you or your child has symptoms that could be from a food allergy, your or your child's health care provider will probably refer you to an allergist for testing. An allergist is a doctor who specializes in diagnosing and treating allergies and asthma.

The allergist will pick the type of food allergy test that's right for you or your child. Tests include skin tests, blood tests, and a test where you eat small amounts of a suspected food while a provider watches for signs of allergy.

Food allergy testing is used to help find out if you or your child has an allergy to a specific food. It is mainly used for people who have had symptoms that could be a food allergy. Testing may also be used to see if allergies have gone away over time.

Food allergy testing can help tell whether you have a true food allergy or a food intolerance or food sensitivity, which may cause similar symptoms. The key difference is that food allergies involve your immune system and can affect your whole body and become life-threatening. But food intolerance and sensitivity don't become life-threatening and generally affect only your digestion.

Examples of food intolerances, or food sensitivities, include lactose intolerance, gluten sensitivity, and irritable bowel syndrome. The symptoms may include belly pain, nausea, gas, and diarrhea, which can also happen with food allergies.

You or your child may need food allergy testing if either of you:

• Have symptoms within minutes to hours after exposure to certain foods. Symptoms may affect your digestion, skin, and/or breathing, and may include:
  • Nausea and vomiting
  • Stomach pain
  • Diarrhea
  • Tingling in the mouth
  • Skin reactions, such as hives or itching.
  • Red, itchy skin or a rash
  • Coughing
  • Stuffy, itchy, or runny nose
• Have had symptoms of anaphylaxis. Symptoms of this life-threatening reaction may appear within minutes to hours after exposure to certain foods. Symptoms include:
  • Trouble breathing
  • Dizziness
  • Fainting
  • Swelling of the tongue, lips, and/or throat
  • Rapid heart rate
  • Cold, clammy, skin that may appear grayish, bluish, or pale

If someone has symptoms of anaphylaxis, call 911 to get medical help right away.

You may also have food allergy testing if you or your child has been diagnosed with eosinophilic esophagitis (EoE). Testing is done to find out which foods may make this condition worse.

Your child's provider may recommend food allergy testing if your infant or child has been diagnosed with:

• Moderate to severe eczema
• Enterocolitis, inflammation of the colon and small intestine
• Enteropathy, a disease of the intestine
• Allergic proctocolitis, a disorder that involves streaks of blood and mucus in stool (poop)

An allergist will ask about your or your child's symptoms, family health history, and medical history, including other allergies. A physical exam is usually done before allergy testing.

Next, your allergist or another provider will do one or more allergy tests. There are many types of allergy tests, and they have different risks. So, ask your provider which tests are best for you or your child. These are the most common tests:

• A skin prick test is the most commonly used test. A provider will place a drop of liquid on the skin of your arm or back. The liquid contains a protein from a specific food that may trigger an immune reaction. The provider will prick the skin under the drop so the liquid gets below the surface. Then you'll wait for 15 to 30 minutes. If a red, itchy bump forms, you may have an allergy to that food. More than one food protein may be tested.

• An allergy blood test measures immunoglobulin E (IgE) antibodies in your blood. Your immune system makes specific types of IgE in response to different foods. If you have a food allergy, your levels of IgE related to that food may be higher than normal. But the amount of IgE in your blood can't confirm a food allergy or tell you how serious an allergy may be. A blood test may be done with other tests to confirm a food allergy.

  To take blood sample, a health care professional will insert a small needle into a vein in your arm. A small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out.

• An oral food challenge test is the most accurate food allergy test. It can be used alone to diagnose food allergies. During this test, you will slowly eat increasing amounts of a food that's suspected of causing your symptoms. You'll be closely watched for an allergic reaction. If your body doesn't react to the food, you aren't allergic to it.

  If you have an allergic reaction, your food allergy is confirmed, and you'll be treated right away for the reaction. The treatment will depend on how severe your reaction is.

• A food elimination diet is a test you do at home following instructions from your allergist. You'll start by removing all suspected foods from your diet for about two weeks. Then you'll slowly start adding the foods back to your diet, one at a time. If you have symptoms when you start eating a food again, you may be allergic to that food. Your symptoms could also be caused by a food intolerance, so other tests may be needed.

  A food elimination diet may not be safe for someone who has had a serious allergic reaction to food in the past.

If you are having any type of allergy test, you may need to stop taking certain medicines and/or supplements before the test. Your provider will let you know what to avoid and for how long. Don't stop taking any medicines unless your provider tells you to. Your test may require other preparation, so be sure to follow all your provider's instructions for getting ready.

A skin prick test can cause itchy or irritated skin. Your allergist may recommend medicine to relieve the symptoms. The test is generally safe, but a severe reaction is possible.

A blood test has very little risk. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

An oral challenge test can cause a severe allergic reaction. That's why this test is done with close supervision by an allergist who can treat you if there is an emergency.

An elimination diet may cause a serious allergic reaction. Ask your allergist what to do if you develop symptoms.

A food challenge test is the only food allergy test that can confirm a diagnosis of a food allergy. If you have other tests, your or your child's allergist will use your test results along with your symptoms and medical history to make a diagnosis.

If the allergist diagnoses a food allergy, the treatment is to avoid the food that trigger your symptoms. There is no cure for food allergies. Avoiding trigger foods involves carefully reading food labels. You'll also need to explain the allergy to anyone who may prepare or serve food to you or your child, including friends, waiters, babysitters, and teachers.

Your allergist will tell you how to manage a mild allergic reaction. In case you or your child has a severe allergic reaction, your allergist may prescribe an autoinjector. An autoinjector is a small device that you use to inject an emergency allergy medicine, called epinephrine. If you need to use the device, it's still very important to get medical help right away even if you feel better. Your allergist will explain when and how to use an autoinjector.

If you have questions about test results and/or how to manage allergic reactions, talk with your allergist.