Dermatitis

Diagnosis

Often, the most important part of treatment is proper diagnosis: identifying what is causing the problem. At Mayo Clinic, the doctor starts by listening to the patient describe the problem and then examining the skin. Sometimes the doctor may need to remove a small sample of skin to examine under a microscope (biopsy). The doctor may also order patch testing, a procedure in which a number of patches are applied to the skin (usually on the back). Each patch contains small amounts of different substances commonly found in the environment. The purpose is to identify the substance causing an allergic response.

Patch Testing

Patch testing is designed to identify substances that may be causing allergic contact dermatitis. During patch testing, multiple disks containing potential allergens are applied to the back. The disks remain in place for about 48 hours. After the disks are removed, the skin is examined for allergic reactions.

Patch testing tries to identify substances causing allergic contact dermatitis.

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Patch testing does not involve scratches or pricks to the skin. It does not identify allergies to food, oral medications, or inhaled substances.

How Is Patch Testing Done?

Patch testing involves a series of appointments, each lasting approximately 20 minutes.

Day 1
During the first appointment, a member of the health care team applies several adhesive strips to the back. Each strip contains 10 dime-sized aluminum disks, each of which contains a different substance. (Occasionally, the disks are applied to another area of the body.)

Day 3
After about 48 hours, the patient returns for disk removal and an examination for reactions such as redness, inflammation or swelling at the patch-test site.

Day 4
The patient may be asked to return after about 72 hours to have the patch test site examined again.

Day 5
Another examination will be done after about 96 hours, since a skin reaction may take that long to appear.

What Do the Results Mean?

If patch testing reveals an allergy to a substance or substances, the test is positive. Patients are given information about the substance(s) that caused the skin reaction, including alternate names of the substance and products which contain the substance.

Even if the result is positive, it can be hard to determine exactly what product is causing a reaction and whether other factors also are involved. It may take time to lessen or eliminate symptoms. It is important to be patient and continue to work with the health care provider to determine the best ways to manage the condition.

If the skin shows no reaction to patch testing, the results are negative. Negative results help eliminate the tested substances as sources of symptoms.

Patch testing has very few risks or side effects. Itching may occur at the patch-test site after testing, but typically goes away within a few days.