Which method is used to apply an allergen to a patient's skin for allergy testing?

Patch testing is a method used to identify allergens that can cause contact dermatitis by applying small amounts of allergens to the skin using adhesive patches. These patches are typically placed on the patient's back and left in place for several days to allow for a reaction to develop. This method is particularly useful for identifying delayed-type hypersensitivity reactions.

Though other methods, such as skin prick testing, also involve applying allergens to the skin, patch testing specifically assesses for reactions that occur over a longer period, distinguishing it from immediate reactions observed with other techniques. Intravenous testing is not typically used for allergy testing, and subcutaneous injections are primarily used for allergen immunotherapy rather than for testing. Thus, patch testing is a well-established method for specifically assessing allergic reactions over time.