What is patch testing?
A patch test is a procedure to determine whether a specific substance (such as nickel, rubber, adhesives, preservatives etc.) causes allergic inflammation of the skin known as allergic contact dermatitis or ACD. During the testing small amounts of different chemicals (that cause ACD) are placed on the back. The intention is to find out which chemical causes a skin reaction.
People with ACD get a skin reaction when they come in contact with the substance they are allergic to. The reaction causes a rash that can be itchy, painful, cracked or even bleed. Common substances that cause ACD can be ingredients in jewelry, makeup, shampoo, medications, cleaning supplies, rubber products and many other household/workplace products.
How is patch testing done?
Testing requires at least three visits to the allergist’s office. Patches used for the testing include most of the common chemicals responsible for ACD. The patches are placed on the back during your visit to the allergist and kept in place for 48
hours. At the second, visit 48 hours later, the patches are removed and a preliminary reading is done. The final reading is done during a third visit 24-48 hours after the preliminary reading.
Precautions to take during the test
- Stop using oral or topical steroids (after consulting with the prescribing doctor) two weeks prior to patch testing
- Avoid tanning two weeks prior to and two weeks after the test
- If there is excessive back hair, please shave with an electric razor one or two days prior to your test
- Test area should be free of oils, lotions and ointments
- Avoid getting the patches wet (take sponge bath instead of a shower)
- Avoid vigorous exercise that may cause you to sweat
- Do NOT erase the numbers/marks we place on your back, that help us interpret the results of the test
What do the patch test results mean?
If you test positive during the test, your doctor will discuss what substance(s) you are allergic to and also provide information about avoiding those substances.