Methylchloroisothiazolinone/Methylisothiazolinone (CMIT/MIT)

Methylchloroisothiazolinone/methylisothiazolinone (CMIT/MIT, CAS 55965-84-9) is the 3:1 aqueous blend of two isothiazolinone biocides, supplied as a low-use-level, broad-spectrum preservative for water-based formulations. It is the chemistry behind preservative systems comparable to Kathon CG. A few parts per million protect a formula against bacteria, yeast, and mold — which is why formulators reach for it when they need wide microbial coverage without loading the product with preservative.

What CMIT/MIT does and why formulators specify it

The two actives work by an electrophilic mechanism: the isothiazolinone ring reacts with thiol groups in microbial enzymes, shutting down cellular respiration and growth. That mode of action is non-specific, so a single low-dose addition covers Gram-positive and Gram-negative bacteria, yeast, and fungi in one shot. Because it is effective at single-digit-to-low-double-digit ppm of active, it adds almost nothing to formulation cost or to the finished product’s sensory profile. The trade-off is that the same reactivity that kills microbes makes it a skin sensitizer above threshold — so the entire value of this chemistry depends on dosing it correctly and within the limits that govern your product class.

Applications

Personal care and cosmetics

CMIT/MIT is a workhorse preservative for rinse-off personal care — shampoo, conditioner, body wash, and hand soap — where short skin contact and dilution suit its profile. Use levels are tightly regulated and vary by region; under EU cosmetics rules the blend is permitted in rinse-off products only, at a maximum of 15 ppm, and it is no longer permitted in leave-on products such as lotions and creams. Other jurisdictions set their own limits. Treat those numbers as moving targets: confirm the current limit for your market and product type against the SDS and the applicable regulation before you formulate, because this is one of the most actively re-evaluated preservative chemistries in cosmetics.

Wet wipes and tissue products

Water-loaded substrates — baby wipes, surface wipes, cosmetic tissues — are a high-risk format for microbial growth, and CMIT/MIT has historically been a common preservative here. Wipes are a leave-on-adjacent format and a known historical driver of contact-allergy cases, so regional restrictions hit the category hard; verify what is currently permitted for the wipe type and market you sell into.

Household, industrial, and in-can preservation

Outside personal care, the same blend preserves water-based industrial systems where regulatory limits are different and use levels are typically higher. It is widely used for in-can (in-tin) preservation of latex paints, coatings, and adhesives — protecting the wet product on the shelf, distinct from a dry-film fungicide — and for microbial control of metalworking fluids, coolants, and process waters that would otherwise sour and grow biofilm. For these applications, dose and handling are governed by the industrial SDS, not the cosmetic limits above.

Forms and grade

The material ships as a stabilized aqueous solution. The most widely specified cosmetic grade is supplied at roughly 1.5% total active isothiazolinones in water (the chemistry behind systems comparable to Kathon CG); higher-active industrial concentrates also exist for in-can and process-water use. Because it is sold as a dilute solution, the active you dose into a finished formula is a small fraction of the as-supplied liquid — check the exact active content and recommended addition rate on the CoA and SDS for the specific grade quoted, since these differ between cosmetic and industrial supply.

Safety and regulatory — the honest version

CMIT/MIT is a recognized skin sensitizer and contact allergen. The same reactivity that makes it an efficient biocide at low ppm drives the regulation: use levels are capped, and for some product classes and regions the blend is restricted or banned outright (notably leave-on cosmetics in the EU). That does not make the chemistry unusable — it remains heavily used and well understood — but correct dosing, current regulatory checking, and proper handling are non-negotiable. We make no safety or efficacy claims here: the Safety Data Sheet and the regulation applicable to your product and market govern permitted concentrations, hazard classification, and handling.

Sourcing CMIT/MIT preservative in bulk

RawSource sources MCI/MI preservative — an isothiazolinone system comparable to Kathon CG — in bulk for cosmetic, personal-care, and industrial formulators and purchasing teams. Send us your target active content, grade (cosmetic vs. industrial), pack size, and destination, and we will quote against your specification with a current SDS and Certificate of Analysis. Use the RFQ form to request a quote.

Kathon is a trademark of its respective owner and is referenced here nominatively only, to identify a comparable isothiazolinone (CMIT/MIT) preservative chemistry. RawSource is not affiliated with, endorsed by, or sponsored by the trademark owner.