Contact allergy to methylchloroisothiazolinone/methylisothiazolinone in north-eastern Italy: a temporal trend from 1996 to 2016

Background Methylchloroisothiazolinone (MCI)/methylisothiazolinone (MI) (Kathon (R) CG) is a common preservative used in industrial products, owing to its strong biocide effect. Contact allergy to MCI/MI has been reported in different occupations, including mechanics, hairdressers and healthcare workers. Objective To retrospectively analyse the temporal trend of MCI/MI sensitization in north-eastern Italy and to evaluate the associations with occupations in our geographical area. Methods From 1996 to 2016, 27 381 patients with suspected allergic contact dermatitis were patch tested in eight departments of Dermatology or Occupational Medicine in north-eastern Italy. Individual characteristics were collected through a standardized questionnaire. Results The overall prevalence of MCI/MI sensitization was 4.2%, with the highest prevalence found in women and in patients younger than 25 years. MCI/MI sensitization was significantly associated with atopic eczema (OR: 1.34, 95% CI: 1.10-1.70), hand/forearm dermatitis (OR: 1.20, 95% CI: 1.05-1.36) and face dermatitis (OR 1.30, 95% CI: 1.10-1.40). There was a significant association between MCI/MI sensitization and chemical processing workers (OR 1.74, 95% CI: 1.03-2.94), while mechanics and healthcare workers resulted more sensitized to this hapten only in the last 3 years. Conclusion Sensitization to MCI/MI is rising in the last years in Triveneto region, the 'epidemic' of sensitization to MCI/ MI is mainly driven by extra-occupational dermatitis, and sensitization in some occupational groups is emerging only in the last years. A full labelling is compulsory for all products that contain isothiazolinones, to permit to identify the culprit agent.