When certain substances come into contact with your skin, a rash can develop due to an allergy. Patch testing is designed to identify the exact cause of the reaction.
The test checks for allergic reaction in response to 36 different allergens from wool and rubbers to plants and resins. This type of testing is used by a dermatologist to test patients diagnosed with allergic contact dermatitis. During the test, the patient will have tiny amounts of substances applied to the skin and fixed with non-allergic tape.
After two days, the physician will remove the patches and examine the skin for any reactions. The patient is then reexamined two days after the initial examination to check for any delayed breakouts. From there, the dermatologist can make a diagnosis and begin the next phase of treatment.