Patterns of simultaneous patch test reactions to thiurams and dithiocarbamates in 164 patients

Background. Thiurams and dithiocarbamates are structurally related sensitizing rubber accelerators. Objectives. To study patterns of simultaneous patch test reactions to thiurams and dithiocarbamates at the Finnish Institute of Occupational Health in 1991-2015. Methods. We searched the patch test files for patients with allergic reactions to thiuram mix, its four components, and three dithiocarbamates, and analysed patterns of simultaneous reactions to these test substances. Results. We found 155 patients who reacted positively to at least one thiuram or dithiocarbamate in the rubber chemical series. Thirty-four (22%) of these patients reacted positively to some dithiocarbamate derivatives. Twenty-one reacted positively to zinc dimethyldithiocarbamate, 20 to zinc diethyldithiocarbamate, and 1 to zinc dibutyldithiocarbamate. All dithiocarbamate-allergic patients reacted positively to some thiurams, and their thiuram reactions were often strong or extreme positive. Nine thiuram mix reactions turned out to be false-positive reactions, without reactions to the constituents, and 24 patients showed false-negative reactions to thiuram mix during the same time period. Conclusions. Dithiocarbamate contact allergy was always connected to thiuram allergy. Screening dithiocarbamate allergy with carba mix thus appears to be unnecessary, but ways to improve the present thiuram mix should be investigated. Meanwhile, individual thiurams are best for diagnosing contact allergy to these accelerators.