Allergic contact dermatitis from the preservative 1,2-benzisothiazolin-3-one (1,2-BIT; Proxel): a case report, its prevalence in those occupationally at risk and in the general dermatological population, and its relationship to allergy to its analogue Kathon CG.

Occupational contact allergy to 1,2-benzisothiazolin-3-one (1,2-BIT, Proxel) is analysed. This compound is widely used in industry as a preservative in water-based solutions such as pastes, paints and cutting oils. The optimal concentration for patch testing proved to be 0.4 g/l (0.04%) in water. In 4 out of 17 patients (23%) at occupational risk (painters, paper-hangers), contact allergy to 1,2-BIT was found. Of 556 consecutive dermatological patients without clear occupational risk, 10 (1.8%) showed positive patch tests to 1,2-BIT; in 3 patients 1,2-BIT contact allergy was related to domestic paper-hanging. Although the chemical structure of 1,2-BIT shows some analogy with the preservative Kathon CG, true cross-sensitivity was found to be unlikely.