Patch testing

Patch testing is a process to detect allergic contact dermatitis to something a person has contacted at home, leisure or at work. Patches with test substances in small chambers or discs are applied to a person’s back. The allergens applied are tailored to the individual. A standard baseline series of allergens is applied, together with other specific allergens relevant to the individual. No needle prick is involved in this procedure. The patches applied so are kept undisturbed for 48 hours, and skin reactions if any graded at the time of removal. A second reading is taken again after 2 days. This technique thus identifies the specific allergen that causes irritant or contact allergy in an individual. This includes allergy to hair dye, shoes, active ingredients, preservative and fragrances in sunscreens, cosmetics and medicaments. Patch testing does not test for urticarial (hives) or food allergy.