How Doctors Test for Skin Allergies

The Basics

When patients visit an allergist to help control their breakouts, allergic reactions or asthma, the allergen skin test is one of the crucial steps they can expect to face. Although semi-invasive, the skin test is simpler than many other medical procedures--just prepare to spend at least a couple hours to get it done.

The Procedure

In allergen skin tests doctors place small amounts of various allergens on the skin, followed by a prick with a special lancet designed for allergen tests. This is mostly done on a patient's back, but doctors will also do it on the upper inside arm. Using this method, one to 40 items can be tested at a time.

Substances Tested

Cat and dog dander, grass and tree pollen and mold spores are among the most commonly tested substances in any allergen test. Doctors also will test for common food allergies, including milk, eggs, wheat flour, fish and peanuts. Where necessary, tests for different fruits and vegetables will be added. Doctors will also test a clear control solution of the lance, to make sure that no allergic reaction is coming from the device. Most doctors have commercially prepared, purified allergens for this purpose.

The Follow-Up

After the skin is pricked and the allergens applied, the doctor will have the patient wait a short period of time--typically, 15 to 20 minutes--and then examine his back for wheals (raised marks on the skin), hives or reactions to each allergen. Doctors will also measure the wheal diameter in millimeters, which reveals the severity of the allergy.

Warnings and More

If a patient has ever had anaphylaxis in response to an allergen--such as a severe reaction to nuts, for example--even a skin-prick test should be avoided. Physicians must frequently assess a severely allergic person's ability to withstand the testing. If this is part of your history, be sure to disclose it. Also, avoid any antihistamine medications, such as Benadryl, three days before allergen skin testing. Your physician also will inform you need to avoid other prescribed medications. Be sure to follow these directions closely.

Skin prick testing is generally safe and has caused very few deaths, but your allergist should have antihistamines and adrenaline available in case of any generalized reactions.

Resources

• Allergy testing
• Food Allergy Testing