Patch tests or Epicutaneous tests:
It is a method by which we can determine/identify the allergens that comes in contact with the skin of a patient and causes inflammation (contact dermatitis). This test is used to diagnose the delayed type of hypersensitivity or Non IgE mediated allergy. If the reaction is involved with the immune system then it is called Allergic contact dermatitis.
Conversely if the skin symptoms result of direct effect of an irritant but there is no involvement of the immunological mechanism then it is termed as Irritant Contact Dermatits(ICD). Small patches usually circular disk filled with different allergens is stick on the back of the patient and left for 48 hours and then result is recorded. According to the type of reaction doctor can interpret the patent either has allergy or not to the particular allergen.