These tests use extracts (a concentrated liquid form) of common allergens such as pollen, mold, dust mites, animal dander, and foods. Once those get in your skin, they could trigger a rash. Your skin will get irritated and may itch, like a mosquito bite.
That reaction is how the doctor can tell you're allergic to something. When you have an allergy, your immune system will make antibodies and set off chemicals to fight off the trigger.
What Happens During a Skin Test?
The steps vary depending on what type of test you're having. There are three main ways to get allergens to react with your skin.
Scratch test, also known as a puncture or prick test: First, your doctor or nurse will look at the skin on your forearm or back and clean it with alcohol. They'll mark and label areas on your skin with a pen. Then they'll place a drop of a potential allergen on each of those spots. Next, they'll scratch the outer layer of your skin to let the allergen in. (It's not a shot, and it won't make you bleed.)
Intradermal test: After they look at and clean your skin, the doctor or nurse will inject a small amount of allergen just under your skin.
Patch test: Your doctor could put an allergen on a patch and then stick that on your arm or back.
Plan for an hour-long appointment. The pricking part of scratch and intradermal tests takes about 5 to 10 minutes. Then you'll wait about 15 minutes to see how your skin reacts.
Patch tests take more time, and two visits to your doctor. You'll have to wear a patch for about 48 hours in case you have a delayed reaction to the allergen.
How to Get Ready for a Test
Tell your doctor about all medicines you're taking, including over-the-counter products. Some drugs can affect the results, so your doctor will give you a list of medicines to avoid before the test.
If you can't stop taking a medication, your doctor or nurse may do a separate test to find out if that drug will hamper the results.
Since allergy medicines, such as OTC antihistamines, stop allergic reactions, you shouldn't take them for a few days before your appointment. You need to let your body react to the allergens in the test.
Is It Safe?
A skin test may be mildly irritating, but most people say it doesn't hurt. Although you're coming into contact with things you could be allergic to, they're very small amounts.
After Your Test
If you get a patch test, you'll go home with bandages on your skin. Don't get these areas wet -- no baths or swimming. When you go back to the doctor in a couple of days, they'll take another look at your skin.
Your doctor or allergist will use the results of your test to come up with a treatment plan for you.