Methylchloroisothiazolinone/methylisothiazolinone contact sensitization: diverging trends in subgroups of IVDK patients in a period of 19 years

Background. The preservative methylchloroisothiazolinone (MCI)/methylisothiazo- linone (MI) is an important allergen, and has thus been subject to regulation in some areas of exposure, mainly in cosmetics. Objectives. To examine whether a decline in sensitization prevalence and intensity of elicitation (by the patch test) can be observed, either overall, or in certain subgroups defined by causative exposures. Methods. On the basis of long-term contact allergy surveillance data collected by the Information Network of Departments of Dermatology (www.ivkd.org), 19922010, in the course of 171 883 consultations, the time trend of (different grades of) positive patch test reactions to MCI/MI (0.01% aqua) was examined in an age-stratified analysis. Results. The overall frequency of positive patch test reactions was 2.33% (95% confidence interval 2.262.4%). No significant overall trend of positive reactions or of the distribution of +, ++ and + + + reactions (p > 0.05) was observed, similarly to what was found for patients in whom cosmetics were recorded as causative exposure (p = 0.55). In contrast, in patients with occupational contact dermatitis who were < 40 years of age, a significant increase in prevalence, by 0.87 percentage points per decade, was identified (p = 0.018). Conclusions. Both applications of MCI/MI, cosmetic and industrial, should be the target of further preventive efforts.