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Patch testing can determine if your eczema due to a skin allergy

Patch testing is used to determine if a patient’s itching, rash or eczema is due to a specific allergy to something he or she is applying to the skin or coming in contact with. This type of eczema is called Allergic Contact Dermatitis.

There are literally thousands of chemicals that can cause contact dermatitis, and found in virtually every corner of the environment in which we live and work. The most common cause of this skin allergy includes jewelry (nickel, gold), perfumes, components in rubber, preservatives in medications, certain topical medications, lanolin, insect sprays, leather, and others.

Patch testing is different from scratch tests performed by allergists. Scratch testing actually 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 a Skin Allergy or Allergic Contact Dermatitis?

Eczema is a red, scaly and itchy eruption, and 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.

How is Patch Testing Performed?

Patch testing involves the application of a small amount of a variety of chemicals to the back. This is covered by a tape and the chemicals are left in the same position for 48 hours. During this time, one cannot get the back wet. Patients should not take a shower during this time, but can wash carefully in a bath (avoiding the back of course).

Patients should also try to avoid exercising or moving excessively during the 1st two days of the test so the tape does not become dislodged from the back.

If you are allergic to one of the chemicals applied to the back, an irritation or area of Eczema will develop around that chemical. This may become somewhat itchy. It is important to avoid scratching as this may dislodge the tape and interfere with the patch test.

After two days, the tape is removed and a reading is performed to determine if you are reacting to any of the chemicals. Some allergies take 3 or 4 days to develop. Therefore, another reading is performed 1 or 2 days later. The back has to be kept dry for the first two days only.

Are there any downsides to Patch Testing?

If patch testing shows that you are allergic to a specific chemical, this may not necessarily mean that this is the chemical that caused your Eczema. In some cases this is regarded as an incidental finding. For example, you are found to be allergic to a preservative in a specific medication, but you have not used this medicine recently, then this is likely not the cause of your Eczema.


If you would like more information, or if you would like to schedule a consultation with one of our experienced dermatologic surgeons, please contact us today.