Your doctor may diagnose dermatitis after talking to you about your signs and symptoms and examining your skin. He or she may also suggest doing a skin biopsy or other tests to help rule out other skin conditions.
If your doctor thinks you have contact dermatitis, he or she might conduct patch testing on your skin. In this test, small amounts of various substances are applied to your skin under an adhesive covering.
During return visits over the next several days, your doctor examines your skin to see if you've had a reaction to any of the substances. This type of testing is best done at least two weeks after your dermatitis has cleared up. It's most useful for determining if you have specific contact allergies.