Methylisothiazolinone (MIT)CAS 2682-20-4
American Contact Dermatitis Society's 2013 "Allergen of the Year" — top sensitizer in water-based paint.
Toxic Chemical Databases
Substance-specific listings — these flags are for Methylisothiazolinone alone, not for the broader family.
Chemical Type
Isothiazolinone Preservative
Chemical Description
MIT became the dominant preservative in water-based paint, latex caulk, and personal-care products after EU regulations restricted older biocides. The shift backfired: MIT turned out to be one of the most aggressive contact allergens on the market, with rapidly rising sensitization rates from the 2010s onward. EU classifies pure MIT as a Category 1B respiratory sensitizer and a severe skin sensitizer; the EU restricted leave-on cosmetic use in 2017 after sensitization rates among consumers crossed 10%. Once sensitized, contact with any MIT-containing product triggers dermatitis — and MIT is in essentially every water-based building product on shelves.
Biological Activity
Severity scores specific to this substance, NOT the parent family average. Differences between siblings are real and meaningful.
Top Health Consequences
- Top contact dermatitis trigger in industrialized countries (declared 2013 Allergen of the Year)
- Lifelong skin sensitization once triggered — no spontaneous de-sensitization
- Asthma in painters from aerosolized water-based paint
- EU Category 1B respiratory sensitizer
- Even "low-VOC" paint typically contains MIT preservative
Pathways of Exposure
- Inhalation during water-based paint roller or spray application
- Dermal contact with painted walls during cure window
- Skin contact with treated water-based caulks and sealants
- Leave-on personal care products (EU-restricted, not in US)
Building Materials with Methylisothiazolinone
Listed alphabetically — product categories where this specific substance appears.
Cooling Tower Water Treatment
Wallpaper Adhesives
Water-Based Caulks & Sealants
Water-Based Latex Paint
Water-Based Wood Stains