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What is patch testing for contact allergic reactions?

Dr. Michael Roizen, MD
Internal Medicine

If you already know what is causing your rash, say a new soap or the ring you bought on the street that contains nickel, you can do things to avoid it so your rash doesn’t come back. But for those who have no idea what’s causing their reaction, an allergist can perform a patch test to (hopefully) isolate the pesky allergen that is causing your discomfort. There are two techniques:

1) A drop of a liquid containing the suspected allergen is dropped onto the skin (usually on your arm or back, depends on how many you’re testing). Your doc will then prick the area. If the skin turns red and blotchy, that indicates the possible presence of an allergy. Possible is key here; skin tests do yield many false positives.

2) A small amount of the potential allergen is injected under the skin. If a lump appears at the site of the injection, you are judged to have tested positive. The bigger the lump, the stronger the liability.

And don’t worry, these unpleasant red bumps aren’t permanent. They’ll heal and disappear about a week after the test. There is a controversy over how valid this type of testing is.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.