The dramatic increase in the rate of methylisothiazolinone contact allergy in Belgium: a multicentre study.

Background: The rate of contact allergy and allergic contact dermatitis caused by methylisothiazolinone (MI) is dramatically increasing throughout Europe. Objectives: To report on methylchloroisothiazolinone (MCI)/MI and MI allergy in Belgium. Patients and methods Between January 2010 and December 2012, the medical charts of 6599 patients of the Belgian Contact and Environmental Dermatitis Group were retrospectively reviewed for MCI/MI and MI sensitization by use of a standardized questionnaire. Available data on sensitization in 2081 patients tested in 2013 were also included. Results: In 2012, the sensitization rate for MCI/MI had increased to 4.5% and that for MI to 6.0%; the latter showed a further increase to 7.2% in 2013. The people mainly affected were women with a median age of 49 years with hand and/or facial dermatitis, most often resulting from the use of cosmetics. Simultaneous reactions to octylisothiazolinone were observed. Conclusion: A dramatic increase in the rate of contact allergy caused by MI in cosmetics is occurring in Belgium. Notwithstanding the recent recommendation to discontinue the use of MI in leave-on cosmetics, safer use concentrations should also be determined for rinse-off products. Close monitoring of MI sensitization in the near future will be necessary, and the highest test concentrations reported for MI and MCI/MI should be included in the baseline series.