Methylchloroisothiazolinone (CMIT)CAS 26172-55-4
The chlorinated cousin of MIT — three times stronger as a sensitizer, sold as the "Kathon" mix.
Toxic Chemical Databases
Substance-specific listings — these flags are for Methylchloroisothiazolinone alone, not for the broader family.
Chemical Type
Chlorinated Isothiazolinone (Kathon Mix)
Chemical Description
CMIT is sold almost exclusively as a 3-to-1 mixture with MIT, branded as Kathon CG and similar preservatives. The chlorine substitution makes CMIT a stronger biocide than pure MIT — and a stronger sensitizer too, roughly three times as potent per unit mass for contact dermatitis endpoints. EU classifies the CMIT/MIT mixture as a Category 1A respiratory sensitizer. The mixture is restricted in EU leave-on cosmetics and limited in concentration even in rinse-off products. Used in water-based paint, building product preservation, and cooling tower water treatment.
Biological Activity
Severity scores specific to this substance, NOT the parent family average. Differences between siblings are real and meaningful.
Top Health Consequences
- Severe skin sensitization — stronger than MIT by ~3x
- EU Category 1A respiratory sensitizer (occupational asthma)
- Cross-reacts with MIT-sensitized patients
- Severely restricted in EU leave-on cosmetics
- Co-formulated with MIT in Kathon mixture
Pathways of Exposure
- Off-gassing from freshly applied water-based paint
- Inhalation during cooling-tower aerosolization
- Skin contact with rinse-off personal care products
- Dermal contact with water-based construction adhesives
Building Materials with Methylchloroisothiazolinone
Listed alphabetically — product categories where this specific substance appears.
Cooling Tower Biocide
Industrial Hand-Soap Concentrates
Water-Based Construction Adhesives
Water-Based Latex Paint (Kathon-preserved)
How We Keep Methylchloroisothiazolinone Out of a House
We do not knowingly install anything containing Methylchloroisothiazolinone. Our specifications name the chemistry we refuse, every submittal is screened against it, and substitutions are rejected — which is how a toxin free home stays that way through construction.
If you want a house specified this way from the start, or an existing house assessed for what is already in it, that is the work we do. Earth Bound Homes builds in Atherton, Palo Alto, Redwood City and across the San Francisco Bay Area.