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Patch Testing

What is Patch Testing?

Patch testing is one of several different types of allergy testing methods, which can determine the cause of an allergic rash, or contact dermatitis (see Rashes). Patch tests are performed with standardized concentrations of chemicals from our daily environment that come into contact with the skin, and that are known, through extensive research and testing, to commonly cause contact dermatitis. Patch testing does not test for food allergies or respiratory allergies.

Why do patch testing?

Patch tests may identify either the cause of or a significant flare factor for a variety of eczematous (rashy) conditions, including rashes of the face, eyelids, scalp, hands and feet, as well as over the entire body. Makeup/cosmetic dermatitis, allergic hair dye reactions, hand and foot eczema, and metal allergic reactions may all be better understood by utilizing patch test procedures. Patients with recurrent episodic flares of an acute rash or with a chronic persistent rash are patch test candidates.

How are patch tests performed?

Standard patch test allergens are applied in the office to the skin of the upper back or upper inner arm, and covered with a hypoallergenic tape membrane. Additional allergens may be selected for testing as history dictates. The patch tests should be kept dry for 48 hours, at which time the patch tests are removed in the office and the test sites examined. A subsequent return appointment should be planned for 2 to 4 days later, so that delayed reactions can be identified and recorded. A positive reaction consists of a persistent red and itchy rash at an allergen site. A positive reaction can be attributed to a specific chemical or group of chemicals, and relevance of the positive reaction to daily exposures can be explored.

Will patch testing cure my rash?

Patch testing is a procedure to identify substances (allergens) to which you are allergic. It assists in the diagnosis of the rash, but patch testing is not a treatment for the rash. The test allergens are representative of the most common contact allergens in North America.

A positive reaction to any given test allergen indicates that you are allergic to the substance, although allergic sensitization may have occurred many years ago and the allergy may not be relevant to your current condition. For example, if you are patch test allergic to two different substances, but never come in contact with one of them, then the positive patch test to that substance can be deemed irrelevant to your situation. If you currently contact the second substance to which patch testing has indicated that you are allergic, then that positive reaction would be relevant. The information gained would help direct you in your attempts to avoid significant allergens.

Unfortunately, patch tests do not test for all possible causes of contact dermatitis. Every day we are exposed to thousands of chemicals, and contact dermatitis is possible from almost any contactant.

How can Cary Dermatology Center help me?

Our doctors are experienced in the use of patch tests to uncover the cause of your contact dermatitis. More importantly, we are committed to the task of determining the best ways to identify, treat and prevent your dermatitis. Please schedule a consultation with one of our doctors to determine if patch testing can be helpful for you.

Contact Us

We encourage you to contact us whenever you have an interest or concerns.

Please call (919) 467-8556.
You can now also text our office at (919) 467-8556.

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Cary Dermatology Center and Cary Aesthetic Center


7:00 am-5:00 pm


7:00 am-5:00 pm


7:00 am-5:00 pm


7:00 am-5:00 pm


7:00 am-5:00 pm