Patch-testing patients' own products: a practical overview for clinicians

Patch tests are the gold standard in the work-up of allergic contact dermatitis. Apart from commercial products, it is also of utmost importance to include the patients' own products. Products with unknown content or containing strong irritant, corrosive, toxic or poisonous chemicals should never be patch-tested, though. Recommendations on how to patch-test finished products can easily be retrieved in the literature and in specialised reference books; practical advice on test modalities (test methods, concentrations, vehicles) have been outlined for leave-on and rinse-off cosmetics, household detergents, chemical products (glues, paints), solid materials (gloves, shoes, textiles, leather goods, metal, plastic and rubber items), occupational products, plants, woods and food items. Separate guidelines exist on how to patch-test drugs. Whenever a positive or negative reaction to a product is obtained, practitioners should always question the possibility of a false-positive or a false-negative reaction, respectively. In these cases, additional test procedures may be required (eg testing of separate ingredients, repeated open-application tests, serial dilutions of a chemical or product, glove-repeated application tests). In this article we provide a practical overview for clinicians on how to test patients' own products.