Propylene Oxide
- Other solvents
- CAS 75-56-9
- IUPAC: 2-Methyloxirane
Propylene Oxide (CAS 75-56-9) appears in 1 of the 2,179 car-care products CarCareTruth tracks (as of August 2026). It is listed on California's Proposition 65 and classified as a VOC.
California Prop 65 listed as a carcinogen. In motor oil and other petroleum-derived products, propylene oxide is not an active ingredient — it appears, when it appears at all, as a trace residual from base-stock refining or ethoxylated-additive manufacturing at parts-per-million levels.
Propylene oxide is a reactive epoxide used industrially to manufacture polyether polyols and propylene glycol. It is classified by IARC as Group 2B (possibly carcinogenic to humans) and is listed on California's Proposition 65 list as a carcinogen.
In finished automotive fluids, propylene oxide is not an intentional additive. When an SDS discloses it under state right-to-know or Prop 65 reporting requirements, it typically reflects a trace residual from petroleum refining or from the manufacture of ethoxylated/propoxylated additive components, present at concentrations far below any level that would register on a GHS hazard classification for the finished mixture.
A Prop 65 disclosure for trace propylene oxide does not by itself mean a finished product poses a meaningful cancer risk in normal consumer use, but it is a legitimate regulatory disclosure and the rubric translates it as a concentration-tiered health-score deduction rather than omitting it.
Health & environment profile
- VOC
- yes
- Prop 65 listed
- yes
- Asthmagen
- no
- EPA Safer Choice
- no
- Aquatic toxicity
- no
- Biodegradable
- yes
- Bioaccumulative
- no
- Persistent
- no
- Ozone depleting
- no
- Microplastic
- no
- PFAS
- no
- Env. score
- 2/5
Common questions about Propylene Oxide
- What is Propylene Oxide used for in car care?
- Trace processing byproduct found in some petroleum-refined base stocks and ethoxylated additive chemistry; not an intentional ingredient.
- Is Propylene Oxide a VOC?
- Yes. Propylene Oxide is classified as a volatile organic compound (VOC).
- Is Propylene Oxide on California's Proposition 65 list?
- Yes. Propylene Oxide appears on California's Proposition 65 list.
- Is Propylene Oxide biodegradable?
- Yes. Propylene Oxide has a confirmed biodegradable profile.
1 product contain this
Prop 65
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.