Late patch test reaction to Disperse Orange 1 not related to active sensitization

One of the most important adverse consequences of patch testing is active sensitization, when subjects previously not allergic become sensitized to one or more of the test chemicals by the test procedure. The allergic test reaction then shows up about 10 or more days (late reaction) after the test application. Sometimes, however, late reactions are seen without active sensitization being present, as some allergens are known to give late reactions in the absence of active sensitization. Here, we describe a female patient shown to be allergic to Disperse Orange 1 from previous patch testing, who was only positive at patch test readings on D7 on the first test occasion and on D14 when patch tested repeatedly.