Methylisothiazolinone

Also referred to as MI, or Kathon CG (when in an ingredient blend)

Used as a preservative when combined with methylchloroisothiazolinone

Is a well-known skin sensitizer

Limited use in leave-on products at 7.5 ppm (parts per million) and rinse-off products at 15 ppm when in a blend

Methylisothiazolinone (MI or MIT) is a skin sensitizing, organic compound used as a preservative in personal care products, including skin care and hair care products, although it originated as a preservative for industrial and household applications.

MI often works alongside methylchloroisothiazolinone (MCI) to help keep formulas free of microorganisms, like bacteria and fungi. Kathon CG is the most common trade name for the blend of these two ingredients.

Countless studies demonstrate the sensitizing effects of MCI and MI on skin, which include irritation, redness (on lighter skin tones) and darkened, grey or purple patches (on darker skin) and dryness.

Methylisothiazolinone isn’t a common preservative in skin care; however, product regulations, especially European Union led, are currently set on reducing the occurrence and concentrations of the compound in rinse-off skin care products (like cleansers) and offering both required and voluntary bans on the ingredient in leave on products (like moisturizers). These regulations stem from MI and MCI’s effects on skin and the body.

Currently the Cometic Ingredient Review Expert Panel only approves of usage of MI and MCI in rise-off products at 7.5 ppm and leave-on products at 15 ppm.

As you can see, MI isn’t worth it. There are many other stable, skin-safe preservatives that formulators can choose from.

See: Methylchloroisothiazolinone