Kathon preservative is a mixture of 2-methyl-4-isothiazolin-3-one (MI) and 2-methyl-5-chloro-4-isothiazolin-3-one (CMI) along with inorganic salt stabilizers, typically in a ratio of CMI:MI = 3:1.^[1] Kathon is an excellent bactericide, widely used in cosmetic products, shampoos, and conditioners as a preservative to inhibit microbial growth. It effectively suppresses yeast, fungi, Gram-negative bacteria, heterotrophic bacteria, algae, and more, making it extensively applied in sterilization and preservation across industries such as textiles, papermaking, petroleum refining, cosmetics, detergents, oilfield water injection, and wastewater treatment.

Pure Kathon is a colorless transparent liquid, while the industrial grade is typically an aqueous solution. Due to varying impurities, its appearance ranges from pale yellow to amber, with a mild odor. It has a relative density (20/4°C) of 1.19, viscosity (23°C) of 5.0 MPa·s, freezing point of -18 to -21.5°C, and pH of 3.5–5.0. It is soluble in water, low-carbon alcohols, and ethylene glycol. The optimal usage pH is 4–8; stability decreases when pH > 8. It maintains high activity with minimal loss when stored at room temperature for one year or at 50°C for six months, though activity declines under high-temperature storage. It is compatible with anionic, cationic, non-ionic, and various ionic emulsifiers, as well as proteins.