At a glance
| Chemical family | An inorganic metal oxide (Sb₂O₃) used as a flame-retardant synergist; a trivalent antimony compound |
| CAS number | 1309-64-4 |
| Classification | IARC Group 2A — probably carcinogenic to humans (2022, upgraded from Group 2B in 1989). NTP: reasonably anticipated to be a human carcinogen. California Proposition 65 listed |
| Where you encounter it | A synergist paired with halogenated flame retardants in mattress foam, upholstered furniture, textiles and carpeting; also used to make some PET plastics |
| Sleep micro-environment relevance | Non-volatile, but migrates out of treated foam and fabric into air and house dust — the main exposure route is inhaled or ingested dust |
| Activated carbon capture | Not the relevant control — as a dust-bound particulate, it is managed by HEPA vacuuming, damp dusting and product choice, not air-phase adsorption |
What it is
Antimony trioxide (Sb₂O₃) is an inorganic white solid — a trivalent antimony compound and a high-production-volume industrial chemical. Its defining role is as a flame-retardant synergist: combined with a brominated or chlorinated flame retardant, it sharply increases the system's fire resistance, so the antimony and the halogenated compound are deployed together across plastics, rubber, textiles and foam. Regulatory — California OEHHA, Prop 65
The hazard picture sharpened recently, and it is worth stating precisely. In 2022 the International Agency for Research on Cancer re-evaluated antimony and placed trivalent antimony — which includes antimony trioxide — in Group 2A, probably carcinogenic to humans, on the basis of limited evidence for lung cancer in exposed people, sufficient evidence in animals, and strong mechanistic evidence. Peer-reviewed — IARC Monographs Vol. 131 That was an upgrade from the Group 2B classification it had held since 1989 — a detail that matters, because older summaries still cite the lower category. The U.S. National Toxicology Program independently lists it as reasonably anticipated to be a human carcinogen. Regulatory — NTP Report on Carcinogens
How it relates to the bedroom
A synergist in the fire-safety system
Mattresses and upholstered furniture have long had to meet flammability standards, and antimony trioxide has been one of the workhorses behind that — not as the flame retardant itself, but as the partner that makes a halogenated flame retardant effective enough to pass. Regulatory — California OEHHA Because of that, it has been present in mattress foam, upholstery, carpeting and textiles for decades. The regulatory tide has now turned: California's Assembly Bill 2998, effective January 2020, bans the sale of foam in mattresses, upholstered furniture and certain children's products for residential use if they contain more than 0.1% of antimony trioxide and certain related flame-retardant chemicals. Regulatory — California OEHHA
Exposure is through dust, not the air you smell
Antimony trioxide is not volatile, so it does not contribute to a "new" smell. Instead, it migrates slowly out of treated foam and fabric and ends up in air and settled house dust, which is then inhaled or transferred from hands to mouth — a route that matters most for crawling children. Regulatory — California OEHHA This is the same exposure pathway as the brominated and organophosphate flame retardants elsewhere in this Atlas: the chemistry leaves the product and concentrates in the dust on floors and surfaces. Inferred — shared dust-migration pathway across flame retardants
The firefighter's footnote
There is a second, blunter way people meet antimony, and IARC names it directly: firefighters are among the occupationally exposed groups, because antimony is released in combustion. Peer-reviewed — IARC Vol. 131 The chemical is added to materials precisely so they resist ignition, and when those materials do burn, the antimony goes into the smoke. For the bedroom that is a footnote rather than the headline — the everyday exposure is dust — but it is a real reminder that fire-safety chemistry and combustion chemistry are two sides of the same coin. Inferred — connecting the synergist's use to its presence in combustion products
What the research says
- It is probably carcinogenic to humans. IARC Group 2A as of 2022 (up from 2B in 1989); lung cancer the human signal. Peer-reviewed — IARC Vol. 131
- U.S. authorities concur. NTP: reasonably anticipated to be a human carcinogen; California Prop 65 listed. Regulatory — NTP; OEHHA
- It is a flame-retardant synergist that migrates into dust. Used in mattress foam, upholstery and textiles; reaches air and house dust. Regulatory — California OEHHA
- It is being regulated out of mattress foam. California AB 2998 bans it above 0.1% in residential mattress foam and upholstered furniture. Regulatory — California OEHHA
What helps reduce it
Choose products without added flame retardants where the law allows. Newer California-compliant mattresses and upholstered furniture should not contain antimony trioxide in foam above the 0.1% limit; a furniture flame-retardant label (TB117-2013) tells you whether flame retardants were added. Regulatory — California OEHHA
Control dust. Because the exposure is dust-bound, the effective routine is HEPA vacuuming, damp dusting and damp mopping, and washing hands before eating. Regulatory — California OEHHA
Mind the youngest sleepers. Hand-to-mouth contact makes dust control most important where infants and children sleep and play. Inferred — from the hand-to-mouth dust-ingestion route
What does NOT help
- Air fresheners or carbon filters. Antimony trioxide is a dust-bound particulate, not an air-phase gas, so odour control and gas-phase adsorption do nothing for it. Inferred — from its non-volatility
- Relying on old "Group 2B" reassurance. The classification was raised to 2A in 2022; assessments that predate that understate the current evidence. Peer-reviewed — IARC Vol. 131
Open research questions
- Typical antimony trioxide concentrations in bedroom dust from legacy (pre-ban) mattresses and furniture, and how quickly they decline as products turn over. Speculation
- The contribution of the bedroom specifically, versus the wider home, to total household antimony dust exposure. Speculation
Citations
- IARC (2022). Cobalt, Antimony Compounds, and Weapons-Grade Tungsten Alloy. IARC Monographs Volume 131. Trivalent antimony (including antimony trioxide) classified Group 2A, probably carcinogenic to humans — upgraded from Group 2B (1989). Summary in The Lancet Oncology (Karagas et al., 2022). iarc.who.int Peer-reviewed
- California OEHHA, Proposition 65. Antimony Trioxide fact sheet — listed carcinogen; flame-retardant synergist in furniture, textiles, carpeting and mattress foam; migrates into air and dust; California AB 2998 (January 2020) bans >0.1% in residential mattress foam and upholstered furniture. p65warnings.ca.gov Regulatory
- U.S. National Toxicology Program (2018). Report on Carcinogens Monograph on Antimony Trioxide — reasonably anticipated to be a human carcinogen (sufficient animal evidence plus mechanistic data). ntp.niehs.nih.gov Regulatory
Frequently asked questions
What does antimony trioxide do in a mattress?
It is a flame-retardant synergist. On its own it is a weak flame retardant, but combined with a halogenated (brominated or chlorinated) flame retardant it makes the system far more effective, so the two are used together in foam, textiles and upholstery. It is not the flame retardant itself so much as the partner that makes the flame retardant work. California now bans foam in mattresses that contains more than 0.1% of antimony trioxide and certain related flame-retardant chemicals.
Is antimony trioxide a carcinogen?
In 2022 the IARC upgraded trivalent antimony, which includes antimony trioxide, to Group 2A — probably carcinogenic to humans — based on limited evidence of lung cancer in exposed humans, sufficient evidence in animals, and strong mechanistic evidence. That is a step up from its 1989 Group 2B classification. The U.S. National Toxicology Program also lists it as reasonably anticipated to be a human carcinogen, and it is on California's Proposition 65 list. This is one of the more genuinely-monitored compounds in the Atlas.
How would I be exposed to it in the bedroom?
Mainly through house dust. Antimony trioxide is not volatile, but it migrates out of treated foam and textiles into air and settled dust, which is then breathed in or transferred from hands to mouth — a particular consideration for crawling children. The exposure route is the same as for many flame retardants: the chemistry leaves the product and ends up in the dust on the floor and surfaces.
How do I reduce antimony trioxide exposure?
Two levers: choose products without added flame retardants where the law allows, and control dust. Newer California-compliant mattresses and upholstered furniture should not contain it in foam above the 0.1% limit, and a furniture flame-retardant label (TB117-2013) tells you whether flame retardants were added. For dust, vacuum with a HEPA filter, damp-dust and damp-mop regularly, and wash hands before eating — the standard, effective routine for dust-bound flame retardants.
Related compounds
Embr is a sleep environment company researching and addressing the chemistry of the bedroom. Research and product development in progress.
Last reviewed 2026-06-27. If you find a factual error, contact us.