Contact sensitization to benzisothiazolinone: IVDK-data of the years 2002 to 2021

Background: Benzisothiazolinone (BIT; CAS no. 2634-33-5) is used as a biocide in various products, including water-based paints, metalworking fluids, and household products. In recent years, increasing sensitization rates have been observed in Europe.Objective: To describe a time trend of sensitization to BIT, analyse concomitant reactions, and identify patients with increased risk of BIT sensitization.Methods: Retrospective analysis of data from 26 739 patients patch tested with BIT, sodium salt, 0.1% petrolatum as part of several special test series within the Information Network of Departments of Dermatology (IVDK), 2002 to 2021.Results: Positive reactions to BIT were noted in 771 patients (2.9%). Sensitization frequency varied over time and increased in recent years, peaking at 6.5% in 2020. Painters and metalworkers handling metalworking fluids, but not cleaners, had a significantly increased risk of BIT sensitization. From our data, there is no evidence of immunological cross-reactivity between BIT and other isothiazolinones.Conclusion: The increasing frequency of sensitization justifies adding BIT to the baseline series. More research on the clinical relevance of positive patch test reactions to BIT and the cause for the rising numbers of BIT sensitization is needed.HighlightsFrequency of sensitization to BIT has increased in recent years.The increasing frequency of sensitization justifies adding BIT to the baseline series.Painters and metalworkers handling metalworking fluids, but not cleaners, has a significantly increased risk of BIT sensitization.We found no evidence of immunological cross-reactivity between BIT and other isothiazolinones.