Methylisothiazolinone, MIT, or MI, is the organic compound with the formula S(CH)2C(O)NCH3. It is a white solid. Isothiazolinones, a class of heterocycles, are used as biocides in numerous personal care products and other industrial applications. MIT and related compounds have attracted much attention for their allergenic properties, e.g. contact dermatitis.

Methylisothiazolinone is used for controlling microbial growth in water-containing solutions. It is typically used in a formulation with 5-chloro-2-methyl-4-isothiazolin-3-one (CMIT), in a 3:1 mixture (CMIT:MIT) sold commercially as Kathon. Kathon is supplied to manufacturers as a concentrated stock solution containing from 1.5–15% of CMIT/MIT. Kathon also has been used to control slime in the manufacture of paper products that contact food. In addition, this product serves as an antimicrobial agent in latex adhesives and in paper coatings that also contact food.

Hazards

MIT is allergenic and cytotoxic, and this has led to some concern over its use. A report released by the European Scientific Committee on Cosmetic Products and Non-food Products Intended for Consumers (SCCNFP) in 2003 also concluded that insufficient information was available to allow for an adequate risk assessment analysis of MIT.

Rising reports of consumer impact led to new research, including a report released in 2014 by the European Commission Scientific Committee on Consumer Safety which reported: "The dramatic rise in the rates of reported cases of contact allergy to MI, as detected by diagnostic patch tests, is unprecedented in Europe; there have been repeated warnings about the rise. The increase is primarily caused by increasing consumer exposure to MI from cosmetic products; exposures to MI in household products, paints and in the occupational setting also need to be considered. The delay in re-evaluation of the safety of MI in cosmetic products is of concern to the SCCS; it has adversely affected consumer safety."

Source and more information: https://en.wikipedia.org/wiki/Methylisothiazolinone