Patch testing is a procedure where allergens are placed on your back for 2 days, then removed. After removal, your back is examined for any reactions. Around two days after removing the patches, you will return to the office again for your second reading. At this time, your provider will determine if it is necessary to perform additional readings after your second reading.
Note that patch testing is not the same as prick testing, which is a different allergy test that is used to diagnose other kinds of allergies, such as hay fever, and is not helpful in diagnosing allergic contact dermatitis.