Patch Testing

Patch testing is a technique used to determine whether a particular substance causes

allergic reaction

in patients. A patch test may be considered for a patient with

dermatitis

potentially caused by a substance at the person’s home or office such as preservatives or fragrances in shampoo or sunscreens, hair dye or chemicals such as nickel. A

dermatologist

undertakes patch testing. Patch testing is used for contact allergies and differs from skin prick testing as it does not test for

hay fever allergies

,

food allergies

or

hives

. Patches are applied with the allergens tailored for the patient across their back. Patches are left on for around five days. Positive allergic reactions will present as a rash of varying irritability. If there are strong positive reactions an ‘angry back’ response can occur where dermatitis flares up creating a false positive result. Further testing may be required to diagnose the particular allergen.