Contact allergy to aliphatic polyisocyanates based on hexamethylene‐1,6‐diisocyanate (HDI)

BACKGROUND: Aliphatic polyisocyanates based on hexamethylene 1,6-diisocyanate (HDI) are components of lacquers, coatings, and spray paints. They are mainly composed of HDI trimers, but also contain larger oligomers, and minute amounts of HDI monomers (<1%). HDI trimers occur as biuret, isocyanurate and asymmetrical types. OBJECTIVES: We report on 4 patients with allergic contact dermatitis/contact allergy resulting from HDI-based polyisocyanates in polyurethane paints. METHODS: The patients were examined at the Finnish Institute of Occupational Health in 2000-2009. The first two patients were diagnosed by testing with their own polyurethane hardeners and ingredients of the hardeners. In 2002, HDI isocyanurate (HDI-IC) trimer was added to our isocyanate series, and the last two patients were screened with the series. RESULTS: Patient no. 1 was exposed and sensitized to HDI biuret trimer, patient no. 2 to HDI-IC trimer, and patient no. 4 to HDI asymmetrical trimer. Patient no. 3 was positive with HDI-IC trimer. He had been handling several paint hardeners containing HDI-based polyisocyanates, but the subtypes of the trimers remained unidentified. All 4 patients were negative with HDI monomer. CONCLUSIONS: HDI trimers are novel contact allergens in workers who handle polyurethane paints. The allergic reactions cannot be explained by sensitization to HDI monomer.