A patch test consists of specific allergens that are applied to small adhesive patches, then placed on the skin (usually the back). If a patched area of skin shows an allergic reaction, such as redness or itchiness, the patient is deemed to be allergic to that substance.
Patch test reactions usually appear quickly – often within 48 hours – though some may take several days. There are a wide variety of allergens that can be tested through patches, including cosmetics, fragrances, foods, chemicals and many more. The materials used in patch testing are hypoallergenic to help rule out conflicting results in the tested areas.
Though patch tests are an important diagnostic tool, they are not foolproof. Some patch test results may return as false-positive and some may return as false-negative. Overall, however, the patch test is a reliable determinant of allergen sources.
Who gets it?
Almost any individual is able to have a patch test.