Methylisothiazolinone, often abbreviated as MI, is a synthetic chemical compound commonly used as a preservative to prevent the growth of harmful microorganisms and extend the shelf life of cosmetic and skincare products. It’s commonly used as a preservative in skincare products including creams, lotions, serums, shampoos and conditioners. MI is known to cause skin irritation and allergic reactions which has led to its restrictions in formulas, with many manufacturers choosing alternative preservatives.