Allergy Testing: Prick Test vs. Patch Test

All of a sudden, it hits you: Your eyes are itchy, your nose is running, and you're sneezing every half-minute. It's easy to write this off as your reaction to the seasons changing, but allergies aren't that simple. They can affect us year-round, showing up in our digestive and respiratory systems, as well as on our skin.

If you're continually suffering an allergic reaction but can't pinpoint the cause, consider asking your doctor for allergy testing. With about 50 million people in the U.S. suffering from nasal allergies alone, you're far from the only person to need testing to find out what ails you.

Allergy tests are performed to determine if a specific substance is causing your symptoms. The most common skin allergy tests are the skin prick test and the skin patch test.

Skin Prick Test

The skin prick test, also known as a puncture or scratch test, is a way for your doctor to determine your sensitivity to inhaled allergens such as pollen, pet dander, or mold. The test can look for allergic reactions of up to 40 different substances at the same time. The skin prick test can also be used to identify food allergies.

The test itself involves the allergist pricking your skin with tiny needles, called lancets, to allow a small amount of allergen to be introduced. Several allergens will be tested on your body as the allergist watches for signs of an allergic skin reaction.

Skin Patch Test

The skin patch test is a type of allergy test used to identify particular substances that cause contact dermatitis (i.e., skin irritation or inflammation due to contact). Patch testing is performed if you have suffered from recent dermatitis or eczema and is the only way to determine the specific irritant substance.

This allergy test usually takes place over the course of two to three office visits. At the first visit, your allergist will apply 20 or more substances in small patches that are taped to the skin of your arm or upper back for 48 hours. During that time, you should avoid bathing, swimming, and activities that cause sweating. When you return for the second visit, the patches are removed and your skin examined for an allergic response to determine which allergens are responsible for your dermatitis. In some cases, the allergist will ask you to come back a couple of days later to check for any delayed reactions.

Preparing for the Test

If your doctor suspects you might have an allergy, you may be referred to an allergist or dermatologist for further testing. Before allergy testing, the allergist will ask you for a thorough medical and lifestyle history, including past illnesses, where you live and work, and your eating habits. Your allergist will also tell you which medicines to avoid before the test to ensure more accurate results.

With both allergy tests, you may experience immune-response symptoms such as itching, a runny nose, watery eyes, or a skin rash. With patch testing, you can expect slightly impaired mobility and minor discomfort for the two days the patches are taped to your skin. Overall, though, these tests are safe and painless procedures.

The Results

A negative test result means that you had no skin changes in response to the allergens. A positive test result is seen as an itchy, red, raised welt, most often signifying that you're sensitive to the test substance. Your doctor may elect to try another type of allergy test to get better results if the test is inconclusive.

Speak to your doctor about which allergy test is best for you and your symptoms. If your allergy test results are positive, your doctor can then determine the allergen source, share ways to avoid it, and suggest medications to ease your symptoms.