Contact Dermatitis Diagnosis

Written by the Healthline Editorial Team | Published on July 10, 2014
Medically Reviewed by George Krucik, MD, MBA on July 10, 2014

Diagnosing Contact Dermatitis

Contact dermatitis is inflammation of the skin that is easily seen and felt. The key to treatment is to identify the source of the problem.

Checking It Yourself

If your hands become red and irritated after regular or prolonged exposure to hot, soapy water or harsh chemicals, you probably already know the cause. If you develop a skin rash, but the cause it not obvious, you may be able to figure it out with a bit of home detective work.

If you notice your hands suddenly become red and tender or have any other symptoms of contact dermatitis, think about what you held or used with your hands that may be the cause. Asking yourself a few simple questions might find the answer:

  • new skin cleanser or lotion?
  • washing dishes by hand?
  • recently working on the lawn?
  • been cleaning the house lately?

If the skin behind your ears and on your wrists becomes irritated, consider perfume or cologne. If a rash encircles your neck, it might be your jewelry or the starch in your collar.


If your rash starts to blister or turn into open sores, you might want to see your doctor to prevent infection or other serious side effects.

Your doctor will ask about what you have come in contact with as well as your history of drug, food, and other allergies. He or she will want to know about any plants, products, or metals you’ve used on the affected area.

If the irritant or allergen is still a mystery, your doctor may order tests.

Patch Test

Allergic contact dermatitis is usually diagnosed with a patch test. This test determines which allergen is the cause of your skin reaction.

For a patch test, a doctor applies tiny amounts of different allergens directly to the patient’s back and covers them with a dressing.  Alternatively, the doctor may use small wells and aluminum patches that are taped to the back.

In both methods, the patches are removed after two days. A reaction—such as skin redness or swelling—will indicate an allergen. If there is no reaction after two days, the spots will be marked and read again after two more days. This is to check for a delayed reaction.

Skin Lesion Biopsy

For repeated, severe cases of contact dermatitis, your doctor might perform a biopsy to rule out other causes. This involves taking a small sample of skin and sending it to a lab for analysis. 

If you have lesions, the doctor may take a small sample from the sore. The sample is usually collected in one of three ways:

Shave Biopsy

Your doctor removes skin from the outermost layer. No stitches are needed. This is the least invasive biopsy method.

Punch Biopsy

A doctor takes a pencil eraser–sized sample of skin using a sharp, hollow instrument. Stitches may be needed, depending on the size of the sample.

Excisional Biopsy

During this procedure, a doctor surgically removes the entire lesion and closes the wound with stitches. For large sections, a skin graft may be needed. 

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