An Italian multicenter study on methylchloroisothiazolinone/methylisothiazolinone contact sensitivity: understanding the structure-activity relationship

The mixture MCI/MI is a well-known contact sensitizer, but studies to determine the primary sensitizer in this blend are rare and performed only in small patient groups. Eight patch-testing Italian clinics conducted a study on 141 patients sensitized to MCI/MI. The patients were patch tested with MCI 0.015% aq, MI 0.005% aq and 0.2% aq. 110 subjects reacted to MCI (42.6% only to MCI, 35.5% to both MCI and MI), while only 16 resulted sensitized exclusively to MI. The Authors discuss the structure-activity relationship of the two molecules to explain the stronger sensitizing capacity of MCI and the possible but not frequent cross reactivity between MCI and MI.