Jozef Jadassohn is the father of patch testing. At the time of his discovery in 1895, he was Professor of Dermatology at Breslau University (now Wroclaw in Poland). He initially reported a patient who had developed an eczematous reaction to mercury plasters. He recognized the potential for eczematous reactions to occur in some (sensitized) patients when chemicals were applied to their skin; he thereby introduced the world to the contact test, then referred to as “Funktionelle Hautprufung.”