Diagnosing whether substances in your environment react with your skin
What is skin contact allergy testing?
Skin contact allergy testing, or patch testing, is a way of diagnosing whether there are substances in your environment that react with your skin to cause allergy symptoms ranging from a rash or hives to chest tightness or difficulty breathing.
Possible allergens include virtually anything your skin comes into contact with:
- Hair and skin care products
- Cleaning and laundry products
- Topical medications
If your history suggests a possible skin contact sensitivity, you may be advised to have patch testing.
What should you expect before, during and after your test?
Patch testing is different from allergy skin testing for inhalants. With inhalant testing, the test substances are placed on the skin, and a reaction occurs or doesn’t occur within 20 minutes. The allergens in patch testing can cause a reaction over a 12-to 24-hour period or more, so the test substances have to be in contact with the skin longer. To make this practical, here’s how the test is performed:
- Test panels of common allergens are attached to medical adhesive paper, with several in each group.
- The panels are placed on the back, between the shoulder blades. They are flat and comfortable to sleep on.
- There are left in place for two to three days, and then removed.
- The first reading is then performed, and a second reading is performed another two to four days later.
Why two readings?
At the time of the first reading, you will have had adhesive paper on your skin for more than 24 hours. The paper alone can irritate the skin, even if there were no allergens present. Sometimes tests that look positive at the first reading calm down and disappear before the second reading. If this occurs, the response was probably inflammation and not true allergy.