Overview
An allergy happens when your immune system overreacts to something harmless.
An allergy skin test identifies what’s triggering that reaction by exposing your skin to small amounts of suspected allergens.
Your immune system normally protects you from germs, but when it mistakes harmless substances like dust or pollen for threats, it can cause allergic symptoms. These can range from sneezing and a runny nose to serious reactions such as anaphylactic shock.
Common Allergens
Allergy testing often checks for reactions to things such as pollen, dust mites, mold, pet dander, foods, insect bites or stings, medications, and household chemicals.
These substances trigger immune responses called hypersensitivities. There are four main types, known as Type I through Type IV. Skin tests usually check for Type I hypersensitivity, which is responsible for most common allergies.
Other names for this test: Type I hypersensitivity skin test, allergy scratch test, allergy patch test, intradermal test, prick test, and puncture test.
Purpose
The test helps diagnose allergies and identify which substances are causing your reactions. With this information, your healthcare provider can recommend a personalized treatment plan.
When It’s Recommended
Your provider may suggest an allergy skin test if you experience symptoms such as a stuffy or runny nose, sneezing, itchy or watery eyes, hives, diarrhea, vomiting, coughing, wheezing, or shortness of breath.
Types of Allergy Skin Tests
1. Scratch (Prick) Test
This is the most common method.
Your provider places small drops of allergens on your skin, usually on your forearm or back, and then gently pricks or scratches through each drop. If you’re allergic, a small red bump called a wheal appears within 15 to 20 minutes.
2. Intradermal Test
This test is mainly used for allergies to insect stings or penicillin, but not food.
Your provider injects a tiny amount of allergen just under the skin’s surface with a fine needle. The area is observed for about 60 to 90 minutes. A red bump or hive indicates a positive reaction. This test is sometimes done when a scratch test is negative but an allergy is still suspected.
3. Patch Test
This test checks for contact allergies, such as reactions to soap, lotion, or cosmetics.
Your provider applies adhesive patches containing small amounts of allergens to your skin. You keep them on for 48 to 96 hours and avoid getting them wet. Afterward, your provider removes the patches and checks for redness, rash, or irritation.
Preparation
Before your test, you may need to stop taking certain medications like antihistamines or some antidepressants. Your provider will tell you which ones to avoid and for how long.
Avoid heavy sun exposure or tanning for at least two weeks before a patch test.
Let your provider know what products you use on your skin and whether you’re around animals regularly.
For children, a numbing cream may be applied to reduce discomfort.
Risks
Allergy skin tests are generally safe and not painful. The most common side effect is mild redness or itching at the test site.
In rare cases, a severe allergic reaction called anaphylaxis can occur. That’s why tests are done in medical offices equipped to handle emergencies.
If you feel intense itching or pain under the patches once you’re home, remove them and contact your provider.
Understanding the Results
A positive result means you developed red bumps or swelling at a test area, showing you’re likely allergic to that substance. A negative result means no reaction occurred, suggesting you’re probably not allergic.
Your provider will interpret your results along with your medical history and symptoms. If an allergy is confirmed, your plan may include avoiding the allergen, taking medication, or making lifestyle changes like reducing dust at home.
If you’re at risk for anaphylactic shock, your doctor may prescribe an epinephrine auto-injector (EpiPen) for emergencies. Use it if you experience severe allergic symptoms and call 911 right away.
When a Blood Test Might Be Used Instead
Your provider may recommend an allergy blood test if you have a skin condition such as severe eczema or psoriasis, if you take medications that could affect the results, or if you’ve had severe allergic reactions in the past.