What is Contact Dermatitis and a Patch Test Clinic?

Patch testing is the standard technique for making a diagnosis of allergic contact dermatitis and determining culprit allergens.

Allergic contact dermatitis can look like a lot of different things. A classic scenario is rash in response to poison oak or ivy. Your provider may consider referral for patch testing when you have a rash that resembles eczema, is new onset, or does not get better with standard therapies.

The goal of the patch test clinic is to identify culprit allergens that can be avoided in the future to prevent flaring of the skin disease. Another name for allergic contact dermatitis is a delayed type hypersensitivity reaction. As such, the patch test process takes place over 3 days (96 hours, usually Monday, Wednesday, Friday) in 1 week. At the last appointment, usually Friday, the results are determined. Our team makes every effort to assess any potential allergens in the testing process. Not everyone who is patch tested will have a positive reaction, however, which may indicate that the rash is not caused by a contact allergen.

Disease Pathogenesis:

New allergens can interact with our skin cells and immune system to trigger an immune response that looks like a rash. When the immune system starts to recognize an allergen and create a reaction, this process is called sensitization. Once someone is sensitized to an allergen, any exposure will set off a skin reaction with contact.


Allergic contact dermatitis often looks like eczema, and can develop at any point in one's lifetime. It is usually pink or red, scaly, and itchy.  


The diagnosis of allergic contact dermatitis is made collaboratively between your primary skin provider and a patch test specialist using patient history, physical exam findings, laboratory (such as biopsy), and patch test results.

Treatment of allergic contact dermatitis is multipronged and aimed at:

  • avoiding any identified allergens;
  • minimizing exposure to new allergens;
  • treating existing inflammation in the skin; and
  • improving the quality of life

Our providers work in partnership with your primary skin provider to find a personalized skin regimen and treat with topical or systemic immunosuppressive or immunomodulatory therapies as needed to control symptoms. By identifying allergens to avoid and creating a personalized skin regimen, we hope to minimize the amount of additional therapy necessary and improve quality of life.

If you or your skin provider suspect allergic contact dermatitis is the cause of your rash, please call 916-734-6111 and request to be scheduled in the Patch Test Clinic.

Peggy Wu, M.D., M.P.H.

Associate Professor of Clinical Dermatology

Department of Dermatology

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