Methylisothiazolinone

Methylisothiazolinone (MIT) is a preservative in the isothiazolinone chemical family used to prevent microbial growth in a variety of consumer products. It is commonly employed alone or in combination with methylchloroisothiazolinone (MCI) in preservative systems such as the MCI/MI blend sold under trade names like Kathon CG. MIT is valued for its broad-spectrum antimicrobial activity and low cost.

MIT has been identified as a potent skin sensitizer. Exposure to products containing MIT can trigger allergic contact dermatitis in some individuals, particularly with repeated or prolonged skin contact. Reactions may include redness, itching, swelling, and vesicular lesions, and can persist or recur with subsequent exposures. Because of its allergenic potential, regulation and labeling of MIT-containing products vary by jurisdiction, and safer alternatives or restricted use are common in many markets.

Regulatory status varies internationally. In several regions, including the European Union, MIT is subject to restrictive use in cosmetics and is largely limited to certain types of products or concentrations, with enhanced labeling requirements and a trend toward reducing or eliminating its use in leave-on cosmetics. Some jurisdictions also require explicit disclosure on ingredient lists and encourage substitution with less sensitizing preservatives.

Identification and consumer guidance. MIT may appear on ingredient lists as methylisothiazolinone, often alongside MCI in mixtures. Individuals with a history of dermatitis or known sensitivity should review product ingredients and consider patch testing under medical supervision if exposure is a concern. In many places, labeling and regulatory guidance help consumers choose products with alternative preservatives.