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2-Octyl-2H-isothiazol-3-one (OIT)

  • Biocides
  • CAS 26530-20-1

2-Octyl-2H-isothiazol-3-one (OIT) (CAS 26530-20-1) appears in 1 of the 2,122 car-care products CarCareTruth tracks (as of August 2026).

Ingredient-level classification is severe at pure-substance concentration: EUH071 (corrosive to the respiratory tract), Acute Tox. 2 (H330, fatal if inhaled), Acute Tox. 3 (H301, H311), Skin Corr. 1 (H314), Eye Dam. 1 (H318), and Skin Sens. 1A (H317). Its own SDS lists a specific concentration limit of >=0.0015% for the Skin Sens. 1A / H317 classification, meaning even trace-level use can trigger a finished product's mixture-level skin-sensitizer classification. At the disclosed use concentration (0.0015-<0.01%), only the skin-sensitization threshold is met; the other ingredient-level hazards (corrosion, acute toxicity) do not carry into the finished mixture's SDS Section 2 classification.

2-Octyl-2H-isothiazol-3-one (OIT) is an isothiazolinone-class biocide related to the more commonly discussed CMIT/MIT preservative pair, but with a distinct (and, at pure-substance concentration, more severe) hazard profile. It is used across paints, coatings, leather goods, and some water-based cleaning concentrates as a preservative against bacterial and fungal growth, typically dosed at homeopathic concentrations of a few hundred parts per million or less.

OIT's own safety data sheet carries a notably severe hazard classification at pure-substance strength, including corrosive and acute-inhalation-toxicity codes. What makes it worth documenting carefully is its specific concentration limit for skin sensitization: OIT's manufacturer data sets the Skin Sens. 1A (H317) classification threshold at as low as 0.0015% by weight, meaning even a homeopathic use level can be the specific ingredient responsible for a finished product carrying a skin-sensitizer classification and label warning. At the concentrations disclosed for consumer car-care use, none of OIT's other severe ingredient-level hazards (corrosion, acute inhalation toxicity) carry into the finished product's own mixture classification, only the skin-sensitization threshold is met. It is not on California's Proposition 65 list.

Health & environment profile

VOC
no
Prop 65 listed
no
Asthmagen
no
EPA Safer Choice
no
Aquatic toxicity
yes
Biodegradable
no
Bioaccumulative
no
Persistent
no
Ozone depleting
no
Microplastic
no
PFAS
no
Env. score
2/5
Purpose: Isothiazolinone preservative used at homeopathic (sub-0.01%) concentration as a microbial growth inhibitor; also the specific ingredient whose Skin Sens. 1A concentration limit (>=0.0015%) drives the finished product's mixture-level H317 classification

Common questions about 2-Octyl-2H-isothiazol-3-one (OIT)

What is 2-Octyl-2H-isothiazol-3-one (OIT) used for in car care?
Isothiazolinone preservative used at homeopathic (sub-0.01%) concentration as a microbial growth inhibitor; also the specific ingredient whose Skin Sens. 1A concentration limit (>=0.0015%) drives the finished product's mixture-level H317 classification
Is 2-Octyl-2H-isothiazol-3-one (OIT) a VOC?
No. 2-Octyl-2H-isothiazol-3-one (OIT) is not classified as a volatile organic compound (VOC).
Is 2-Octyl-2H-isothiazol-3-one (OIT) on California's Proposition 65 list?
No. 2-Octyl-2H-isothiazol-3-one (OIT) is not on California's Proposition 65 list.

1 product contain this

Related

Health and environment notes translate the manufacturer Safety Data Sheet, the GHS classification, and authoritative regulatory listings (California Prop 65, EPA). Not medical advice. They describe the ingredient itself; whether a hazard applies to a finished product depends on its concentration and how it's used.