Methylchloroisothiazolinone Worst Preservative No known benefits Methylchloroisothiazolinone at a glance Also referred to as MCI, or Kathon CG (when in an ingredient blend) Used as a preservative when combined with methylisothiazolinone Is a well-known skin sensitizer Can only be used in leave-on products at 7.5 ppm (parts per million) and rinse-off products at 15 ppm Methylchloroisothiazolinone description In combination with methylisothiazolinone, it goes by the trade name Kathon CG (among others). Introduced into cosmetics in the mid-1970s, it elicited a great number of sensitizations in consumers. This led to it not being included in cosmetics other than rinse-off products. When combined with methylisothiazolinone, methylchloroisothiazolinone offers preservative benefit. This blend is used in many products instead of parabens, despite the fact that parabens have a better safety track record and lower incidence of causing a sensitising reaction. Related ingredients: Methylisothiazolinone