False-Positive "Poral" Cobalt Patch Test Reactions Reside in the Eccrine Acrosyringium

Seventy (32%) of 222 patients patch tested in our contact dermatitis clinic from 1993 to 1995 had irritant reactions to cobalt. These reactions were “poral” and seemed to reflect a unique and probably toxic effect of cobalt on the acrosyringium. The reactions are neither follicular nor petechial and we believe they are not allergic. The histopathology of the reactions is described in detail.