During skin allergy tests, your skin is exposed to suspected allergen-causing substances (allergens) and then monitored for signs of an allergic reaction.
Along with your medical history, allergy tests may be able to confirm if a particular substance you touch, breathe or eat is causing symptoms.
Why is testing necessary?
Information from allergy tests can help your doctor develop an allergy treatment plan that includes allergen avoidance, medications, or allergy shots (immunotherapy).
Allergy skin tests are widely used to help diagnose allergic conditions, including:
- Allergic rhinitis
- Allergic asthma
- Dermatitis (eczema)
- Food allergies
- Allergy to penicillin
- Allergy to bee venom
Skin tests are generally safe for adults and children of all ages, including infants. In certain circumstances, however, skin tests are not recommended. Your doctor may advise against skin testing if:
Have you ever had a severe allergic reaction? You may be so sensitive to certain substances that even small amounts used in skin tests can cause a life-threatening reaction (anaphylaxis).
Take medications that may interfere with test results. These include antihistamines, many antidepressants, and some heartburn medications. Your doctor may determine that it is better for you to continue taking these medicines than to temporarily stop them in preparation for a skin test.
You have certain skin conditions. If eczema or severe psoriasis affects large areas of skin on the arms and spine – common test sites – there may not be enough clear, undeveloped skin to do an effective test. Other skin conditions, such as dermatography, can cause unreliable test results.
Blood tests (tests for antibodies to immunoglobulin E) may be helpful for those who should not or may not have skin tests. Blood tests are not used for penicillin allergy.
In general, allergy skin tests are reliable for diagnosing allergies to airborne substances, such as pollen, pet dives, and dust mites. Skin testing can help diagnose food allergies. But because food allergies can be complex, you may need additional tests or procedures.
Medications which may interfere with the results
Before scheduling a skin test, bring your doctor a list of all your prescriptions and over-the-counter medications. Some medications can suppress allergic reactions, preventing skin testing from yielding accurate results. Other medications may increase your risk of developing a severe allergic reaction during a test.
Because medications are cleared from your system at different rates, your doctor may ask you to stop taking certain medications for up to 10 days. Medications that may interfere with skin tests include:
- Prescription antihistamines, such as hydroxyzine (Vistaril).
- Over-the-counter antihistamines, such as loratadine (Claritin, Alavert), diphenhydramine (Benadryl), chlorpheniramine, cetirizine (Zyrtec Allergy), and fexofenadine (Allegra).
- Tricyclic antidepressants, such as nortriptyline (Pamelor) and desipramine (Norpramin).
- Some heartburn medications, such as cimetidine (Tagamet) and ranitidine.
- Asthma medication omalizumab (Xolair). This medicine may damage the test results for six months or longer even after you have stopped using it. By comparison, most medications affect results on a daily basis.