At a glance
| Chemical family | A hindered-phenol antioxidant (2,6-di-tert-butyl-4-methylphenol); semi-volatile |
| CAS number | 128-37-0 (food additive E321) |
| Classification | IARC Group 3 — not classifiable as to carcinogenicity to humans (limited animal evidence; no human evaluation). A sensory irritant in laboratory assays |
| Where you encounter it | An antioxidant/heat stabiliser in polyurethane foam, rubber and plastics; and — the same molecule — a preservative in foods, fats, oils and cosmetics |
| Sleep micro-environment relevance | Sublimes slowly from fresh foam and has been measured emitting from every urethane cushion tested — but predicted indoor air levels sit well below the irritation threshold |
| Activated carbon capture | As a semi-volatile organic, BHT is readily adsorbed; airing and ventilating new foam handles most of it |
What it is
BHT is a hindered-phenol antioxidant — a molecule whose job is to stop other molecules from oxidising. It has been used since 1947 in rubber, petroleum products and plastics, and since 1949 as an antioxidant in fat-containing foods, edible oils and cosmetics, which is why human exposure to it is so widespread. Peer-reviewed — IARC Monographs Vol. 40 In polyurethane foam it plays the same protective role: a heat stabiliser that keeps the polymer from degrading during manufacture and use. Regulatory — U.S. CPSC
On hazard, BHT is one of the calmer entries in the Atlas. IARC places it in Group 3 — not classifiable as to carcinogenicity to humans — on the basis of limited and inconsistent animal evidence and no data adequate to evaluate humans. Peer-reviewed — IARC Group 3 Tellingly for an antioxidant, when BHT was tested alongside known carcinogens it often reduced their activity rather than adding to it. Peer-reviewed — IARC Vol. 40 European cosmetic regulators reached a similarly measured conclusion: the EU Scientific Committee on Consumer Safety judged BHT safe in cosmetics at up to 0.8% in leave-on and rinse-off products. Regulatory — EU SCCS Opinion
How it relates to the bedroom
The molecule you eat and sleep on
The most useful thing about BHT is the perspective it offers. The compound stabilising your mattress foam is chemically identical to the E321 keeping a box of cereal fresh. Peer-reviewed — IARC Vol. 40 That does not make either use automatically safe or automatically suspect; it means the honest questions are always the same two — how much, and by what route — rather than whether a scary-sounding chemical is "present." Presence is not exposure, and exposure is not dose.
It does off-gas — and here is how much
BHT is semi-volatile: as a solid it slowly sublimes into the vapour phase, and it leaves fresh foam the same way. The U.S. Consumer Product Safety Commission measured BHT emitting from every prime and bonded urethane carpet-cushion sample it tested, with twenty-four-hour emission rates ranging from 0.024 to 0.648 milligrams per square metre per hour. Regulatory — CPSC In a standardised mouse bioassay BHT also behaved as a relatively potent sensory irritant. Regulatory — CPSC Taken alone, those two facts sound concerning.
The calibration is what matters, and CPSC did it. The indoor air concentrations predicted from those emission rates came out several-fold to dozens-fold below the level associated with sensory irritation — the irritation data were roughly seven times higher than the highest predicted residential air concentration and twenty-five times higher than the median. Regulatory — CPSC CPSC's conclusion was that BHT emitted from these cushions would not be expected to cause sensory irritation in the home. Emission rates had also fallen about three-fold over a few years of manufacturing change. Regulatory — CPSC
Why this is the reassuring shape of an Atlas page
BHT is a model of a low-concern off-gassing compound done honestly: it is genuinely emitted, it genuinely has an irritant property in the lab, and the measured-and-modelled dose at home is still comfortably under the line where that property would matter. Inferred — combining the measured emission rates with the irritation threshold Saying so plainly is more useful than either ignoring the emission or inflating it.
What the research says
- Low carcinogenicity concern. IARC Group 3; limited animal evidence; frequently anticarcinogenic alongside other agents. Peer-reviewed — IARC Vol. 40
- It does off-gas from foam. Measured emitting from every urethane cushion tested, 0.024–0.648 mg/m²/h. Regulatory — CPSC
- Predicted home levels are below the irritation threshold. 7–25× margin in CPSC's assessment. Regulatory — CPSC
- Judged safe in cosmetics to 0.8%. Regulatory — EU SCCS
- An emerging, unsettled question — BHT's breakdown products. Recent reviews note that some of BHT's metabolites can be more reactive than the parent compound and have been linked, in mechanistic and animal work, to oxidative stress and possible endocrine effects, with attention focused on pregnancy and early childhood. This remains active debate rather than established risk: a 2022 toxicogenomic assessment found no endocrine activity for BHT or its close analogues. Peer-reviewed — Pu 2025; De Abrew 2022
What helps reduce it
Air out new foam. Because BHT leaves foam by slow sublimation, unwrapping and ventilating a new product, and keeping the room aired for the first days to weeks, removes most of what would otherwise drift into bedroom air.
Favour newer, low-emission foam. Measured BHT emission rates fell about three-fold across a few years of manufacturing change, so lower-emission formulations release less. Regulatory — CPSC
Ventilate. Ordinary fresh-air exchange clears BHT along with the wider new-foam mixture.
What does NOT help
- Treating "it off-gasses" as the whole story. Emission is real, but the dose predicted at home is well below the threshold for the one effect (irritation) that BHT is known to cause at higher levels. Regulatory — CPSC
- Avoiding it on cancer grounds. BHT is Group 3 and is often protective against other carcinogens; cancer is not the concern here. Peer-reviewed — IARC Vol. 40
Open research questions
- Long-term, low-level inhalation of BHT and other semi-volatile foam additives across years of bedroom use. Speculation
- How BHT partitions between foam, bedroom air, and settled house dust over a mattress's life. Speculation
Citations
- IARC (1986/1987). Butylated hydroxytoluene (BHT). IARC Monographs Vol. 40 (p. 161) and Supplement 7 (1987, p. 59) — Group 3 (not classifiable); limited evidence in experimental animals, no evaluation possible in humans. inchem.org — IARC Vol. 40 summary Peer-reviewed
- U.S. Consumer Product Safety Commission. Hazard Assessment of Butylated Hydroxytoluene Emitted from Urethane Carpet Cushions (BHT as a polyurethane-foam heat stabiliser; 24-hour emission rates 0.024–0.648 mg/m²/h; sensory-irritant mouse bioassay; predicted residential air levels 7–25× below the irritation threshold). cpsc.gov Regulatory
- EU Scientific Committee on Consumer Safety. Opinion on Butylated Hydroxytoluene (BHT) (SCCS) — concluded safe as a cosmetic ingredient up to 0.8% in leave-on and rinse-off products (0.1% toothpaste, 0.001% mouthwash). health.ec.europa.eu Regulatory
- Pu M, et al. (2025). Research progress on the human exposure levels and health risks of butylated hydroxytoluene and its metabolites. Zhonghua Yu Fang Yi Xue Za Zhi (Chinese Journal of Preventive Medicine) — review noting that BHT metabolites can be more toxic than the parent compound, with proposed endocrine-disruption, oxidative-stress and DNA-damage mechanisms and a focus on pregnant women and children. Peer-reviewed
- De Abrew KN, et al. (2022). A New Approach Methodology (NAM)-Based Assessment of Butylated Hydroxytoluene (BHT) for Endocrine Disruption Potential. Toxicological Sciences — toxicogenomic assessment finding that neither BHT nor its close analogues connected to estrogen, androgen, thyroid, or steroidogenesis endocrine activity. Peer-reviewed
Frequently asked questions
Is the BHT in my mattress the same as the BHT in food?
Yes — it is the same molecule. Butylated hydroxytoluene (E321) has been used since the late 1940s as an antioxidant in fats, oils, cereals and cosmetics, and the same compound is added to polyurethane foam as a heat stabiliser to keep the polymer from oxidising. The molecule is identical; what differs is the amount and the route of exposure. That is a useful reminder that "a chemical in your mattress" and "a chemical you eat" can be one and the same.
Is BHT a carcinogen?
IARC places BHT in Group 3 — not classifiable as to carcinogenicity to humans. The animal evidence is limited and inconsistent, there was no basis to evaluate human carcinogenicity, and in many experiments BHT actually reduced the activity of other carcinogens, consistent with its role as an antioxidant. It is one of the lower-concern compounds in this Atlas.
Does BHT off-gas from foam, and is that harmful?
It does. BHT is semi-volatile and slowly sublimes from fresh polyurethane foam; the U.S. CPSC measured it emitting from every urethane carpet-cushion sample it tested. BHT is also a sensory irritant in a standardised mouse assay. The reassuring part is the dose: CPSC concluded that the indoor air concentrations predicted from those emission rates sit several-fold to dozens-fold below the level that would cause sensory irritation, so home exposure would not be expected to cause it. Airing out new foam reduces it further.
How do I reduce BHT from new foam?
Because BHT leaves foam by slow sublimation, the same airing-out routine that handles other new-foam emissions works here: unwrap and ventilate a new product, and keep the bedroom aired for the first days to weeks. Measured emission rates from cushions also fell roughly three-fold over a few years of manufacturing change, so newer low-emission foam tends to release less.
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.