There are three types of skin allergy tests used to detect a range of different allergens: patch testing, prick/scratch testing, and intradermal injection. Below, we’ve unpacked all three to explain what they’re used for, what the procedures are like, and what to expect.
Patch tests are typically used to identify allergens that cause allergen contact dermatitis, skin rashes, urticaria, or eczema. During this test, a physician will apply several potential triggers (allergens) to the skin. These allergens are held in place with the use of plates or small dishes and hypoallergenic tape. The plates are taped to a person’s back for 48 hours. At the end of that time, they are removed, and the skin underneath examined. All patients have a follow-up appointment 2-5 days after the initial removal for the dermatologist to make more thorough observations and provide a diagnosis. For more information, see our main resource page about Allergy Patch Testing, or learn about other types of skin allergy tests.
A skin prick test, also known as a puncture or scratch test, is designed to detect immediate allergic reactions, typically to as many as 40 substances at once. The test is often used to identify common environmental allergies, like pollen, mold, pet dander, certain foods, and dust mites. Skin prick tests are generally done on the forearm, but some children may receive the test on their upper back.
The skin prick test involves exactly that: a skin prick. The doctor is not injecting allergens into your bloodstream. Rather, the doctor will clean your skin, place a drop of allergen extract on the arm, and use a lancet to just penetrate the skin’s surface. To avoid contamination, new lancets are used for each allergen. Bleeding is extremely rare, and most patients feel only a mild, momentary discomfort.
Prior to the test, your doctor will usually scratch on two additional substances to ensure your skin will react normally. The first is a histamine, which will cause a skin response in most patients. If your skin does not react to this substance, an allergy test may not reveal sensitivity to an allergen, even if one exists. The second is glycerin or saline, which should not produce a skin reaction. However, if your skin reacts to these substances, it is often an indication that you have sensitive skin. This determination will signal to the doctor that they need to cautiously interpret your results, as not doing so could provide a false diagnosis.
The doctor will wait around 15 minutes after the skin prick before looking for signs of an allergic reaction. If you test positive for any of the allergens, you will generally develop a raised red bump that resembles a mosquito bite. The doctor will note the bump, measure its size, and move on.
Also known as a skin injection test, this type of exam is recommended to check for allergies to insect venom or certain drugs, like penicillin. The most invasive of the three skin allergy tests, this procedure involves using a syringe to inject a very small amount of allergen extract into the skin on your arm (not into a vein). After cleaning the skin and injecting the substance, the doctor will wait for 15-20 minutes to see if an allergic reaction appears.
Based on your suspected allergy, environmental factors, and lifestyle, one of our doctors will recommend a skin allergy test that works for you. Sometimes, however, these tests may be used in tandem with one another. For example, if a substance did not react during the scratch test, but you have reason to believe it could be the cause of your allergies, the doctor may use the intradermal injection test to make a definitive diagnosis.
In all cases, these tests should create only a mild discomfort, and they should never be painful. If you are worried about undergoing an allergy skin test, talk to us about your concerns. And, if you haven’t already, contact us to schedule an appointment. Living with a skin allergy is extremely difficult if you don’t know its cause. We can help provide a diagnosis and develop a life-changing treatment plan.