Mercury allergy in a contact dermatitis clinic in Northern Ireland

441 consecutive patients (294 female, 147 male) with suspected contact dermatitis were patch tested to the European standard series, mercury metal (1% pet), ammoniated mercury (1% pet.), and mercuric chloride (0.1% aq.). 14 patients (3.2%), 12 of whom were female, showed a positive response to 1 or more mercury compounds; none reacted to mercuric chloride alone. Primary sensitization was most likely due to either inoculation with vaccines containing merthiolate preservatives or amalgam dental restorations. Mercury allergy was of historical clinical relevance in only 2 patients, both women who developed gingivostomatitis following insertion of amalgam dental fillings. 1 of these women subsequently developed allergic contact dermatitis from contact lens solutions, shampoos and cosmetics which contained mercury preservatives. On the basis of these findings, we recommend patch testing with both metallic mercury and ammoniated mercury in patients with suspected mercury allergy.