An allergy test is an exam performed by a trained allergy specialist to determine whether your body has an allergic reaction to a known substance. The exam can be in the form of a blood or skin test (prick/patch).

Your immune system is your body’s natural defense. Allergies occur when your immune system overreacts to something in your environment. For example, pollen, which is normally harmless, can cause the immune system to overreact. This overreaction can lead to:

  • a runny nose
  • sneezing
  • blocked sinuses
  • itchy, watery eyes
  • coughing or wheezing

Allergens are substances that can cause an allergic reaction. There are three primary types of allergens:

  • Inhaled allergens affect the body when they come in contact with the lungs or membranes of the nostrils or throat. Pollen is the most common inhaled allergen.
  • Ingested allergens are present in certain foods, such as peanuts, soy, and seafood.
  • Contact allergens must come in contact with the skin to produce a reaction. An example of a reaction from a contact allergen is the rash and itching caused by poison ivy.

Allergy tests involve exposing you to a very small amount of a particular allergen and recording the reaction.

Learn more about insect allergy tests.

Allergies affect more than 50 million people living in the United States, according to the American College of Allergy, Asthma, and Immunology (ACAAI). Inhaled allergens are by far the most common type.

The World Allergy Organization estimates that asthma is responsible for 250,000 deaths annually. These deaths can be avoided with proper allergy care, as asthma is considered an allergic disease process.

Allergy testing can determine which particular pollens, molds, or other substances you’re allergic to. You may need medication to treat your allergies. Alternatively, you can try to avoid your allergy triggers.

Before your allergy test, your doctor will ask you about your lifestyle, family history, and more.

They’ll most likely tell you to stop taking the following medications before your allergy test because they can affect the test results:

  • prescription and over-the-counter antihistamines
  • certain heartburn treatment medications, such as famotidine (Pepcid)
  • benzodiazepines, such as diazepam (Valium) or lorazepam (Ativan)
  • tricyclic antidepressants, such as amitriptyline (Elavil)
  • systemic corticosteroids (if you are undergoing patch testing)

An allergy test may involve either a skin test or a blood test.

Skin tests

Skin tests are used to identify numerous potential allergens. This includes airborne, food-related, and contact allergens. The three types of skin tests are scratch, intradermal, and patch tests.

Your doctor will typically try a scratch test first. During this test, an allergen is placed in liquid, then that liquid is placed on a section of your skin with a special tool that lightly punctures the allergen into your skin’s surface.

You’ll be closely monitored to see how your skin reacts to the foreign substance. If there’s localized redness, swelling, elevation, or itchiness of the skin over the test site, you’re allergic to that specific allergen.

If the scratch test is inconclusive, your doctor may order an intradermal skin test. This test requires injecting a tiny amount of allergen into the dermis layer of your skin. Again, your doctor will monitor your reaction.

Another form of skin test is the patch test (T.R.U.E. TEST). This involves using adhesive patches loaded with suspected allergens and placing these patches on your skin. Patch testing is performed to evaluate for cases of allergic contact dermatitis.

The patches will remain on your body after you leave your doctor’s office. The patches are then reviewed at 48 hours after application and again at 72 to 96 hours after application.

Blood tests

If there’s a chance you’ll have a severe allergic reaction to a skin test or cannot perform a skin test, your doctor may order a blood test.

For this test, a blood sample is tested in a laboratory for the presence of antibodies that fight specific allergens. Called ImmunoCAP, this test is very successful in detecting IgE antibodies to major allergens.

Learn about the difference between a RAST test and a skin test.

If you discover you have an allergy, there are several ways to proceed. If it’s an allergy to a food, it may be as simple as removing that food from your diet.

Other allergies require treatment.

In some cases, your doctor may prescribe medications like antihistamines or corticosteroids.

Another treatment option is immunotherapy, also known as allergy shots. During immunotherapy, you’ll be given shots containing small amounts of the allergen so your body can slowly build up immunity.

For people with life threatening allergies, your doctor may prescribe emergency epinephrine.

There are also a number of home remedies that may help prevent or reduce symptoms of allergies. These include air filters and saline nasal or sinus rinses.

Allergy tests may result in mild itching, redness, and swelling of the skin. Sometimes, small bumps called wheals appear on the skin.

These symptoms often clear up within hours but may last for a few days. Mild topical steroid creams can alleviate these symptoms.

On rare occasions, allergy tests produce an immediate, severe allergic reaction that requires medical attention. That’s why allergy tests should be conducted in a doctor’s office that has adequate medications and equipment, including epinephrine to treat anaphylaxis, which is a potentially life threatening acute allergic reaction.

Call your doctor right away if you develop a severe reaction right after you leave the doctor’s office.

Call 911 immediately if you have symptoms of anaphylaxis, such as:

  • swelling of the throat
  • difficulty breathing
  • fast heart rate
  • low blood pressure

Severe anaphylaxis is a medical emergency.

Once your doctor has determined which allergens are causing your symptoms, you can work together to come up with a plan for avoiding and managing them.

Your doctor can also suggest medications that may ease your symptoms.