Patch Test Instructions

Patch testing helps identify whether your skin rash (dermatitis) may be caused or aggravated by contact allergies. It is not the same as a Skin Prick Test, which is used for hay fever or food allergies.

What to Expect

• Small amounts of 24–80 substances are placed in individual square plastic or round aluminum chambers.

• Chambers are applied to the upper back using hypoallergenic tape.

• The procedure itself takes about 30 minutes, but plan for at least a 1-hour visit.

  • If you are sensitive and react to a substance, you may develop: Red rash (erythematous), Follicular rash, Pustules, Burn-like reactions

• Strong reactions may cause blisters or ulcers. If feels intense itching remove the chamber immediately and apply hydrocortisone cream for relief. Call office. Note: this may leave a permanent scar.

Follow-Up Appointments

• Second appointment (2–3 days later): patches are removed, and reaction are noted.

• Third Appointment is for reading on day 4 or 5. Results are discussed. 

Possible Outcomes

• Positive reaction: helps confirm diagnosis.

• False positives (“angry back”): nearly all test areas become red and itchy.

• False negatives: no reaction, even to substances that usually cause rash.

Testing Instructions

Please notify staff if any of the following apply, as testing may need to be rescheduled:

• Please let us know if you have recently been prescribed prednisone (oral steroids) or a steroid injection, as they can affect patch test results. 

• If you are using topical medications, do not apply them to the back for 5 days prior to your appointment  

• If you use over-the-counter moisturizers, do not apply them to your back for 2 days prior to your appointment  

• Avoid sun exposure to your back for 2 weeks prior to patch testing  

• Antihistamines (i.e. Benadryl, Zyrtec, etc) will not interfere with patch testing. They can be continued if desired.  

Precautions

• After patches are placed it is critical to keep area dry:  

  • Make sure you shower prior to your patch application appointment as showering will not be permitted for 48 hrs to ensure accurate results. Washing hair in a sink and sponge bathing while avoiding the back is OK as long as patches remain dry.  

  • Avoid strenuous activity or exercise that could make you sweat, as well as movements that could cause the patches to come off or dilute the allergens; reinforce loose patches with tape (paper tape preferred)