Octylisothiazolinone (OIT)CAS 26530-20-1
Wood preservative isothiazolinone — added to oil stains and exterior sealers for fungal resistance.
Toxic Chemical Databases
Substance-specific listings — these flags are for Octylisothiazolinone alone, not for the broader family.
Chemical Type
Oil-Soluble Isothiazolinone Fungicide
Chemical Description
OIT is the long-chain (octyl) variant of MIT, used primarily as a fungicide in oil-based wood preservatives, exterior paints, and stains. The octyl side chain makes it oil-soluble, suiting it to solvent-based applications where MIT (water-soluble) doesn't work. Same isothiazolinone sensitization concerns apply, plus persistence on weather-exposed surfaces — OIT-treated wood is still measurably biocidal years after application, with residual exposure to maintenance workers and re-coating crews.
Biological Activity
Severity scores specific to this substance, NOT the parent family average. Differences between siblings are real and meaningful.
Top Health Consequences
- Skin sensitization with rising clinical incidence
- REACH SVHC for sensitization endpoints
- Persistent on exterior wood for years post-application
- Aquatic toxicity in stormwater runoff
Pathways of Exposure
- Skin contact with treated decks, fences, and exterior wood
- Inhalation during oil-based stain application
- Off-gassing from recently-treated wood
Building Materials with Octylisothiazolinone
Listed alphabetically — product categories where this specific substance appears.
Deck Preservatives
Exterior Wood Stains
Oil-Based Wood Sealers
Pressure-Treated Wood (Some Lines)
How We Keep Octylisothiazolinone Out of a House
Octylisothiazolinone is one of the substances our screening is built to catch. A healthy home is won in the specification and the submittal review, long before anyone opens a bucket on site.
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 Menlo Park, Redwood City, San Mateo County and across the San Francisco Bay Area.