Quick Answer
To prepare for a skin prick allergy test, you must stop all antihistamines (including cetirizine, loratadine, fexofenadine) for 5–7 days before the test. First-generation antihistamines need 3–7 days clearance. Most other allergy medications (nasal steroids, inhaled steroids) do not need to be stopped. Tell your allergist all medications you take.
Medications to Stop Before Allergy Skin Testing
The most critical preparation step is stopping antihistamines, which suppress the skin reaction used to identify allergens. If antihistamines are in your system during testing, you may get false-negative results — the skin won't react to allergens you are actually sensitized to, leading to missed diagnoses.
Second-generation antihistamines (cetirizine/Zyrtec, loratadine/Claritin, fexofenadine/Allegra, desloratadine/Clarinex) typically require a 5–7 day washout period before skin testing. First-generation antihistamines (diphenhydramine/Benadryl, chlorpheniramine) need only 3–4 days. The antihistamine H2 blockers used for heartburn (famotidine, cimetidine) also suppress skin reactions and need 48 hours of clearance.
Tricyclic antidepressants (amitriptyline, doxepin) have potent antihistamine activity and may need 7–14 days clearance. Some antipsychotic medications also have antihistamine properties. Always provide your allergist with a complete medication list so they can determine appropriate washout periods for each drug.
Medications That Do NOT Need to Be Stopped
Most other allergy medications do not significantly affect skin test results and do not need to be stopped. These include nasal corticosteroid sprays (fluticasone, mometasone, budesonide), inhaled corticosteroids for asthma (budesonide, fluticasone), leukotriene inhibitors (montelukast/Singulair), nasal decongestant sprays, nasal saline rinses, asthma inhalers (albuterol, long-acting beta-agonists), and montelukast.
Oral corticosteroids do not significantly affect skin prick tests if used at standard doses for short courses but may suppress testing if used at high doses for prolonged periods. Omalizumab (Xolair) significantly suppresses skin test reactivity and should be considered by your allergist when interpreting results. Beta-blockers do not affect test results but are medically significant because they impair epinephrine response in case of a severe reaction during testing — inform your allergist.
- STOP before testing: all antihistamines (5–7 days), H2 blockers (48 hours), tricyclic antidepressants (7–14 days)
- DO NOT stop: nasal steroids, inhaled steroids, montelukast, nasal saline, asthma inhalers
- INFORM your allergist about: beta-blockers, omalizumab, oral steroids, antidepressants
What to Wear and What to Expect
Wear loose clothing with easy access to your arms — skin prick testing is typically performed on the inner forearms, and sometimes the upper back for larger panels. Avoid applying lotions, creams, or topical corticosteroids to the testing area on the day of your appointment, as these can interfere with reactions.
During the test, small drops of allergen extracts are placed on the skin, and a lancet is used to lightly prick or scratch through each drop. The test is typically mild and briefly uncomfortable rather than painful. You will wait 15–20 minutes before the results are read. A small wheal (raised bump) at an allergen site indicates a positive reaction. The control sites — histamine (positive) and saline (negative) — confirm test validity.
Safety and What Happens After the Test
Skin prick testing is very safe — the allergen dose is extremely small and systemic reactions (anaphylaxis) occur in fewer than 0.1% of tests performed in properly equipped allergy offices. All allergy testing facilities maintain epinephrine and emergency equipment. Patients are observed for 20–30 minutes after testing before leaving.
After positive results are identified, your allergist will discuss them in the context of your clinical history. Not every positive test result means you are clinically allergic — asymptomatic sensitization (positive IgE without symptoms) is common. Allergen immunotherapy, medication adjustments, and avoidance strategies will be recommended based on the combination of test results and symptom history.
Key Takeaways
- Stop second-generation antihistamines 5–7 days before skin prick testing to avoid false-negative results.
- Nasal steroids, inhaled steroids, montelukast, and asthma inhalers do not need to be stopped.
- Tell your allergist all medications — including beta-blockers, antidepressants, and omalizumab.
- Wear loose clothing with access to inner forearms; avoid applying topical products to test sites.
- Skin prick testing is safe — anaphylaxis occurs in fewer than 0.1% of tests in allergy offices.
Related Guide
Allergy Testing Methods Guide →