Patch testing – Revisited

Patch testing is a well-established method of diagnosing contact allergy wherein patients with a history and clinical picture of contact dermatitis are re-exposed to the suspected allergens under controlled conditions to verify the diagnosis [1]. The results of first innovative patch-testing technique were presented by the German dermatologist, Josef Jadassohn (1863-1936) in 1895. The safety and efficacy of this diagnostic tool have stood the test of time, and is still the gold standard for the diagnosis of allergic contact dermatitis (ACD). Since its discovery, much effort has gone into understanding the chemical and toxicological aspects of test allergens, in standardization and optimization of allergens, vehicles, and concentrations of patch-test materials, in procedures of its application, as well as in reading and scoring of test reactions-all contributing to the development of an accurate, reliable, and safe test with a high reproducibility of its results. There have also been advances in the field in many areas including our basic understanding of type IV hypersensitivity reactions, emerging contact allergens, irritant contact dermatitis (ICD), systemic contact dermatitis (SCD), patch testing in children, occupational dermatitis, and reactions to biomedical devices. Improved diagnosis and management of contact dermatitis and availability of more comprehensive databases of causative contact allergens enable physicians to manage allergic contact dermatitis (ACD) by advising the patients to avoid the allergens he/she is sensitized to and providing a list of safe products that do not contain these allergens. This contribution is a review of recent literature pertaining to improving patch testing technology.