Methylisothiazolinone (MIT)CAS 2682-20-4

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