Patch testing: Facts and controversies

The German dermatologist, Josef Jadassohn (1863-1936), first presented the results of his innovative patch-testing technique in 1895. The safety and efficacy of this diagnostic tool has 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 been put into standardization and optimization of allergens, vehicles, and concentrations of patch-test materials; in procedures of its application; and 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. Even this seemingly carved-in-stone practice, which has been used for nearly 120 years, has been questioned and challenged, engendering debates, disagreements, and controversies, which show no signs of coming to an end.Almost every step of the procedure has provoked discussions and controversies:
- Who should be patch-tested?
- What should be the criteria for referral of patients to a patch-test clinic?
- What are the criteria for including an allergen in the standard patch-test series?
- Which chambers should be used in terms of size, material, and shape?
- What is the optimal occlusion time?
- What is the optimal test-reading time?
- What is the best way of scoring patch-test reactions?
- How should the relevance of positive patch tests be classified? (This latter issue, which is the crucial and most complex and tricky phase of the process, has paradoxically not created more controversies than other apparently less problematic parts of the procedure.)