Patch testing is used to determine whether your itching, rash, or eczema is the result of a specific allergy to something the skin is coming in contact with. This is a type of eczema called allergic contact dermatitis.
There are thousands of chemicals that can cause contact dermatitis. The most common causes of this skin allergy include:
- Jewelry (nickel, gold)
- Perfumes
- Rubber
- Preservatives in medications
- Certain topical medications
- Lanolin
- Insect sprays
- Leather
Patch testing is different from scratch tests performed by allergists. Scratch testing looks for inhalants (things you inhale, e.g. ragweed, dust) and foods. Patch tests test only for things that touch the skin.
What skin changes are seen with allergic contact dermatitis?
Eczema is a red, scaly, and itchy eruption, the primary rash caused by a contact skin allergy. Eczema may also be caused by many other things besides an allergy, and consequently, patch testing will help determine whether a contact allergy is involved.
The process of patch testing follows these steps:
- A small amount of a variety of chemicals are applied to your back.
- The chemicals are covered by tape and left in the same position for 48 hours. During this time, one cannot get the back wet.
- If you are allergic to one of the chemicals, an irritation or area of eczema will develop around that chemical. This may become somewhat itchy. It's important to avoid scratching, as this may dislodge the tape and interfere with the patch test.
- After 48 hours, the tape is removed and a reading is performed to determine if you are reacting to any of the chemicals. Some allergies take 3-4 days to develop. Therefore, another reading is performed 1-2 days later, but the back only has to be kept dry for the first 2 days.
Interested in seeing whether patch testing could help you take the next step in skin irritation or eczema treatment? Schedule an appointment with one of our board-certified dermatologists at Sanova Dermatology.
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