Patch Testing


In order to identify the cause of contact dermatitis, patch testing can be done. Our dermatology practice in Honolulu can help patients who want to know more about their skin condition. Dr. Matsuda and Dr. Sheu will guide you through the procedure.

What is allergic contact dermatitis?

Allergic contact dermatitis (ACD) is a skin condition where the patient develops patches of eczema (also known as dermatitis) as a response to a specific substance. These patches appear red, inflamed, and can itch. Often they may blister. A substance called an allergen is responsible for the allergies. You are not born with this type of allergy. You may have come in contact with a particular substance that signals your immune system to respond to defend your body.

What is patch testing?

Patch testing is a procedure that is used to identify the external substances that cause a person’s allergies. Patch testing benefits those patients who have had recurrent or chronic contact dermatitis. It is a cost-effective diagnostic tool for ACD patients.

Why is patch testing necessary?

Some people know exactly what they are allegic to and can avoid allergic reactions and ACD. Others have no idea what allergens are causing their dermatitis, so they can be exposed over and over again.
With patch testing, these patients can avoid recurrences of ACD since they will now know which substances to avoid. There are chemicals found in cosmetics, skin creams, rubber, leather, or metals that could be responsible for the breakout of ACD. Although it is not a foolproof test for finding the cause of every dermatitis case, patch testing is helpful for most patients.

How is patch testing done?

The patient first needs to see a dermatologist to check if rashes and other symptoms are due to ACD. Your dermatologist will also be the one to suggest if you need patch testing or not. The procedure involves the following:

  • Small amounts of various potential allergens will be applied on the skin and occluded there for 2 days. They will be fixed using hypoallergenic tape.
  • The potential allergens applied on your skin need to remain in place for at least one day. If you are allergic to a particular allergen, this will produce a positive patch test reaction that will be checked between two to seven days after the initial patch application.
  • Even after removal, the patch test will be read again two to three times up until one week passes.

Which substances will be tested during my patch test?

You will be tested with the most common substances that may be responsible for your ACD. Many substances may not be recognizable, but all of these are commonly found in additives to clothes, leather, ointments, and other everyday necessities. These include:

  • Cobalt
  • Epoxy resin
  • Balsam of Peru
  • Ethylenediamine
  • Formaldehyde
  • Neomycin
  • Paraben mix
  • Plants
  • Formaldehyde resin
  • Wool alcohols (lanolin)
  • Quaternium-15
  • Nickel
  • Fragrances
  • Clioquinol
  • Rubber accelerators

If your dermatologist suspects other substances to be allergens, they may be added to your patch. You may be asked to bring samples of the substances you commonly use at home or at work. Discuss with your dermatologist the last thing you came in contact with before the rash first appeared so it can be tested, too.

What should I expect after my patch test results?

When your dermatologist finds out that you have a reaction to any of the substances that were tested on you, you will be given advice as to how you can avoid those chemicals to prevent flare-ups. If the results show that there is no skin reaction, the possibility of you having ACD could be ruled out.

What should I do if I get a positive result from my patch test?

You may ask your dermatologist for tips on which substances to avoid and how to avoid them. These may include:

  • Carefully reading the list of ingredients found on new products purchased, especially when it comes to cosmetics
  • Applying barrier creams and other protective gear to specifically avoid the allergen
  • Switching to alternative products
  • Discussing with your employer about eliminating the source of allergen, if it is found in your workplace
For more information on Patch Testing and Skin Allergy Treatment, please request a consultation, or call us at (808) 949-7568.