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Allergen Skin Testing

(Allergen Scratch Testing; Allergy Skin Testing; Allergy Scratch Testing)

What Is an Allergen?

An allergen is a substance that triggers an allergic reaction. Common allergens include dust mites, pet dander, mold, insect venoms, foods, medications, and pollen from trees, grass, and weeds.

Reason for the Test

Allergen skin testing is done to determine which, if any, substances trigger allergic reactions in an individual. Once allergic triggers are identified, a person can take the needed steps to avoid or lessen contact with the allergen. Individuals can also receive allergy shots or drops under the tongue to reduce their reaction to allergens.

Symptoms of an allergy may include:

  • Itchy eyes, nose, throat, or skin
  • Nasal and/or chest congestion
  • Runny nose
  • Watery eyes
  • Wheezing/Asthma
  • Hives
  • Atopic dermatitis
  • A severe allergic reaction that can include difficulty in breathing, hives, and other heightened allergy symptoms—anaphylaxis
  • Cramping and/or diarrhea after consumption of certain foods
  • Severe reactions to insect stings

Type of Sample Taken

There is no actual sample taken. A small scratch or skin prick will be given in a designated area of your skin and observed.

Prior to Collecting the Sample

Avoid taking certain medications for 1-3 days before the test, as directed by your healthcare provider.

During the Sample Collection

For the test, a diluted sample of the suspected allergen(s) will be applied directly to your skin, usually on your forearm or back depending on how many tests are done. The substance is either applied to a shallow scratch made on the skin or a skin-prick needle will push the substance into the surface layer of your skin. For every allergen tested, you will have a separate scratch or skin prick.

After Collecting the Sample

You may experience mild irritation where the substance is applied to the skin.

In addition, there is a very small risk of anaphylaxis. Contact emergency medical services right away if you experience the following after your test:

  • Hives and itching
  • Swelling, redness, stinging or burning, especially on the face, mouth, eyes, or hands
  • Lightheadedness, caused by a drop in blood pressure
  • Obstruction of the nose, mouth, or throat
  • Severe respiratory distress
  • Chest tightness, shortness of breath, wheezing
  • Nausea, vomiting, cramping, diarrhea
  • Heart arrhythmias
  • Convulsions
  • Shock

Results

If you are allergic to one of the test substances, redness and swelling, known as wheal and flare reaction, will appear at the site, usually within 15-20 minutes. If you are not allergic to a substance, the site will remain normal.

Many factors can affect the reliability of lab tests. A test may suggest an illness that actually does not exist. This is called a false positive. A test may also miss an illness that actually does exist. This is called a false negative. Another type of allergy skin test, called an intradermal test, may be done if there is a false negative (an allergen is still suspected). It involves an injection of allergen into the skin.

A doctor will consider the results from many tests and your symptoms before making a diagnosis. It is important to discuss these results with your doctor before making any conclusions or beginning any treatment.

REFERENCES:

Allergic rhinitis. EBSCO DynaMed website. Available at: http://www.dynamed.com/topics/dmp~AN~T116217/Allergic-rhinitis. Accessed December 8, 2019.

Allergy testing: Tips to remember. American Academy of Allergy Asthma and Immunology website. Available at: http://www.aaaai.org/conditions-and-treatments/library/at-a-glance/allergy-testing. Accessed December 8, 2019.

Anaphylaxis. EBSCO DynaMed Plus website. Available at: http://www.dynamed.com/topics/dmp~AN~T113858/Anaphylaxis. Updated February 18, 2016. Accessed December 8, 2019.

Li J. Allergy testing. Am Fam Physician. 2002;66(4):621-624.

Last reviewed January 2020 by EBSCO Medical Review Board Mary-Beth Seymour, RN