Patch Tests are used to confirm or rule out contact allergy.
Contact allergy develops slowly. Patch test allows the testing of different materials which are suspected of eliciting contact allergy, such as metals.
If the allergist is concerned about a particular material, it can also be checked individually.
Sometimes there is not a specific suspicion and the patch test is performed with a wide range of allergens, so we can test different materials commonly found to cause contact dermatitis.
In practice, a patch containing the suspected material is adhered to the skin so that the skin is exposed to the tested material. Alternatively, patches containing common allergenic materials are adhered to the skin to scan for an allergenic material. The test should be attached to the back around 48 hours and then the person must return to the allergist (in accordance to a pre-arranged appointment). After removing the patches the allergist will assess the elicited skin reaction.
It is important to note that the patient should avoid wetting his back in those 48 hours when the patch is attached to the skin: the patient should avoid sweating and should shower carefully in order not to wet his back.
Sometimes, after the initial 48 hours, the allergist may ask the patient to come back in another 24 or 48 hours to complete the examination.