At a glance
| Chemical family | The smallest common cyclic volatile methylsiloxane (cVMS); a volatile silicone. Filed here as a VOC for its airborne behaviour, alongside its sibling D5 |
| CAS number | 556-67-2 |
| Classification | Not a carcinogen (not IARC-classified). EU Substance of Very High Concern — persistent & bioaccumulative (PBT / vPvB); harmonised classification "suspected of damaging fertility"; EU endocrine-disruptor listing (contested) |
| Where you encounter it | Personal-care products (antiperspirants, hair and skin care) at lower levels than D5; an industrial silicone feedstock |
| Sleep micro-environment relevance | Evaporates off skin and hair into bedroom air like D5, but at lower product concentrations; being phased out of cosmetics |
| Activated carbon capture | Not the lever — product reformulation (already underway) and lighter use of silicone products address it |
Regulatory & certification status
Where D4 (Octamethylcyclotetrasiloxane) stands across the major regulatory systems and the certifications a bedroom product might carry. Each row links to the governing instrument; where a jurisdiction has no specific measure, that is stated plainly rather than left blank.
| European Union | REACH Substance of Very High Concern on the Candidate List (identified as PBT and vPvB) and restricted under Annex XVII entry 70. The earlier restriction (Commission Regulation (EU) 2018/35) banned D4 and D5 at >=0.1% by weight in wash-off (rinse-off) cosmetic products from 31 January 2020. Commission Regulation (EU) 2024/1328 extended entry 70 to D4, D5 and D6 generally: they may not be placed on the market as substances, constituents or in mixtures at a concentration >=0.1% by weight, applying from 6 June 2026, with later derogated dates for certain uses (e.g. medical devices and human/veterinary medicinal products, and D5 as a dry-cleaning solvent). The draft's separate '6 June 2027 leave-on cosmetics' date was not found in the regulation and has been removed. Harmonised CLP classification (Annex VI, Index 014-018-00-1): Flam. Liq. 3 (H226); Repr. 2 (H361f, suspected of damaging fertility); Aquatic Acute 1 (H400) and Aquatic Chronic 1 (H410, M-factor 10) -- i.e. very toxic to aquatic life with long-lasting effects (the draft's 'Aquatic Chronic 4 / H413' was incorrect). It is not listed under the EU POPs Regulation. Regulatory — EUR-Lex · Intertek bulletin -- EU ad |
| United States | Under TSCA, EPA published a DRAFT risk evaluation for D4 (September 2025) that preliminarily determined the substance presents an unreasonable risk of injury to human health (driven by worker exposure across multiple conditions of use plus one consumer use) and to the environment; this is a draft -- not a final determination or regulatory action -- with a public comment period and peer review pending. D4 is NOT listed on California's Proposition 65 list (verified against the current OEHHA list; CAS 556-67-2 does not appear). Regulatory — US EPA · OEHHA |
| Canada | D4 was added to Schedule 1 (List of Toxic Substances) under CEPA on 4 February 2011, the government having concluded it is harmful to the environment; D4 meets the persistence criterion but not the bioaccumulation criterion under the Persistence and Bioaccumulation Regulations. Risk management is final: a pollution-prevention (P2) planning notice for D4 in industrial effluents was published in the Canada Gazette, Part I, in June 2012 to prevent or minimise releases to the environment. Regulatory — Government of Canada |
| Australia | AICIS (formerly NICNAS) assessed D4 under the IMAP programme, publishing a human-health tier II assessment and an environment tier II assessment (cyclic volatile methyl siloxanes, 2020). No AICIS ban or scheduling restriction on D4 was identified. D4 is an industrial chemical regulated by AICIS rather than an agricultural/veterinary chemical under the APVMA. Regulatory — AICIS |
| United Kingdom | Under GB CLP, D4 carries the inherited EU harmonised classification (Flam. Liq. 3, H226; Repr. 2, H361f; Aquatic Acute 1, H400 and Aquatic Chronic 1, H410, M=10), and the pre-Brexit EU restriction on D4/D5 in wash-off cosmetics was retained in GB law; the EU 2024 extension to D4/D5/D6 across product types does not apply automatically in Great Britain. HSE ran a UK REACH Regulatory Management Options Analysis (RMOA) for D4/D5/D6 with a call for evidence in 2023 (open 2 March -- 1 May 2023) to decide whether further GB restriction or Authorisation-List (Annex 14) action is warranted -- no new GB REACH restriction on D4 is yet in force. Regulatory — HSE (Citizen Space) -- UK · UK legislation |
| Certifications | CertiPUR-US: not specifically addressed -- its prohibited-substances list targets ozone depleters, certain flame retardants, heavy metals, formaldehyde and high VOCs rather than naming D4, though its low-VOC emissions limit could capture D4 off-gassing indirectly. OEKO-TEX Standard 100: D4 is not a named/regulated parameter and is not specifically screened. GREENGUARD/GREENGUARD Gold: a low-VOC emissions certification that measures total and individual VOC emissions but does not certify against D4 as a named compound. Industry — CertiPUR-US · OEKO-TEX |
| The 72-hour test window | Largely captured. D4 is a volatile cyclic siloxane (a cyclic volatile methyl siloxane) that off-gasses readily, so a short ~72-hour emissions chamber test using thermal-desorption/GC-MS can detect it in the vapour phase, unlike heavier non-volatile SVOC additives that migrate mainly into dust. Inferred — from the compound's volatility/emission profile versus the VOC focus of short chamber tests |
What it is
D4 is octamethylcyclotetrasiloxane, the smallest of the common cyclic volatile methylsiloxanes — the silicone family that also includes D5 and D6. It is a volatile, oily fluid used as a carrier and emollient in personal-care products and, more heavily, as a building block for manufacturing silicone polymers. In finished cosmetics it now appears at much lower concentrations than D5, which is the dominant cyclic siloxane in products. Peer-reviewed — Dudzina et al. 2013
The single most important correction this page makes is about its hazard label. D4 is not a carcinogen — it has not been classified as one by IARC or other major bodies, and calling it "Group 2B," as some lists do, is an error. Inferred — D4 is absent from IARC carcinogen classifications; the common "Group 2B" label is a misattribution and is corrected here Its actual regulatory concerns lie elsewhere.
How it relates to the bedroom
The same airborne route as D5
For the sleep environment, D4 behaves like its sibling: it is volatile, so it lifts off skin and hair after a product is applied and enters the air you breathe, rather than depositing on sheets. The practical difference is concentration — because D5 is the predominant cyclic siloxane in modern products and D4 the minor one, the airborne D4 in a typical bedroom is lower than the D5. Peer-reviewed — Dudzina et al. 2013 The pathway, though, is identical, which is why D4 belongs beside D5 in the volatile-organic family rather than among the personal-care residues that linger on fabric.
Why D4 is the more-regulated sibling
Here the two diverge. D5's toxicology is relatively reassuring; D4's is not, and regulators moved against it first. The EU designated D4 a Substance of Very High Concern on the grounds that it is persistent, bioaccumulative and toxic in the environment (PBT) and very persistent and very bioaccumulative (vPvB) — and it carries a harmonised classification as suspected of damaging fertility, plus a listing as an endocrine disruptor. Regulatory — EU REACH Annex XVII entry 70 / ECHA SVHC That reproductive flag has experimental support: unlike D5, D4 shows weak estrogenic activity, binding the estrogen receptor and producing increased uterine weight and estrous-cycle changes in animal studies. Peer-reviewed — Marrugo-Padilla et al. 2024 In fairness, the endocrine-disruptor classification is contested, with a 2024 mechanistic review arguing that D4 lacks estrogen-pathway disruptive potential — so the science is not fully settled. Speculation — D4's endocrine-disruptor status is scientifically debated
Restricted, like D5, for the environment first
D4 sits in the same cosmetic restriction as D5: under EU REACH it may not be placed on the market in wash-off cosmetics at 0.1% or more, a limit later extended to leave-on products, with environmental persistence the primary driver. Regulatory — EU Commission Regulation 2018/35, Annex XVII entry 70 The combination of PBT/vPvB plus the fertility flag is why D4 is being designed out of personal-care formulations faster than its larger sibling. Inferred — the stacked PBT + reproductive concerns drive faster phase-out of D4
What the research says
- Not a carcinogen. Not IARC-classified; the "Group 2B" label is a misattribution. Inferred — corrected here
- EU Substance of Very High Concern. Persistent and bioaccumulative (PBT / vPvB); environmental driver of its restriction. Regulatory — ECHA / EU REACH
- Suspected fertility toxicant. Weak estrogenic activity and reproductive effects in animals — unlike D5. Peer-reviewed — Marrugo-Padilla et al. 2024
- The minor cyclic siloxane in products. Present at much lower levels than the dominant D5. Peer-reviewed — Dudzina et al. 2013
What helps reduce it
Use fewer silicone-heavy hair and skin products. The same lever as for D5 lowers airborne cyclic siloxanes generally. Inferred
Let reformulation do the work. EU restrictions are removing D4 from cosmetics; choosing compliant products accelerates the shift. Regulatory — EU Commission Regulation 2018/35
Ventilate after getting ready. As with D5, airflow disperses the brief post-application spike. Inferred
What does NOT help
- Treating D4 as a cancer risk. It is not a carcinogen; the real flags are environmental persistence and fertility. Inferred
- Laundering bedding. D4 is airborne, not a fabric residue, so washing sheets does nothing for it. Inferred
Open research questions
- Whether D4's weak estrogenic and reproductive effects in animals translate to any human risk at airborne personal-care exposure levels. Speculation
- How quickly product reformulation is reducing residual D4 in cosmetics and indoor air. Speculation
The Embr Exposure Ledger: Octamethylcyclotetrasiloxane (D4)
One chemical, several public questions, answered from independent datasets and joined here — the environment it shows up in, the body burden it carries, how it is regulated, and what actually reduces it.
Detection and body-burden figures are occurrence data, not a personal measurement or a health diagnosis. Part of the Embr Exposure Ledger — an open, cross-dataset chemical join (download the data), reusable with attribution.
Citations
- Commission Regulation (EU) 2018/35 amending Annex XVII to REACH (entry 70); ECHA SVHC listing. D4 (CAS 556-67-2) + D5 restricted to <0.1% in wash-off cosmetics from 31 Jan 2020; D4 = SVHC (PBT/vPvB); harmonised CLP "suspected of damaging fertility"; very toxic to aquatic life. legislation.gov.uk / ECHA Regulatory
- Marrugo-Padilla A, et al. (2024). Toxicokinetic profiles and potential endocrine disruption effects at the reproductive level promoted by siloxanes. J. Appl. Toxicol.. D4 binds ER-α with low estrogenic activity; increased uterine weight and estrous-cycle alterations in rats; reproductive concern (contrast: D5 does not bind the estrogen receptor). Via Consensus. DOI 10.1002/jat.4706 Peer-reviewed
- Dudzina T, von Goetz N, Bogdal C, Biesterbos JW & Hungerbühler K (2014). Concentrations of cyclic volatile methylsiloxanes in European cosmetics and personal care products: Prerequisite for human and environmental exposure assessment. Environment International, 62: 86-94. D5 the predominant cVMS; D4 present at much lower levels — the minor cyclic siloxane in modern products. Via Consensus. DOI 10.1016/j.envint.2013.10.002 Peer-reviewed
Frequently asked questions
What is D4?
D4 — octamethylcyclotetrasiloxane — is the smallest of the common cyclic volatile silicones (cVMS), a close relative of D5. Like D5 it is volatile and was used as a carrier and emollient in personal-care products such as antiperspirants, hair and skin products, and as a building block for making silicones. In modern cosmetics it is present at much lower levels than D5, which dominates, and it is being phased out.
Is D4 a carcinogen?
No. D4 has not been classified as a carcinogen by IARC or other major bodies, and it should not be labelled one — a common error. Its regulatory concerns are different: the EU classifies it as a Substance of Very High Concern for being persistent and bioaccumulative in the environment (PBT and vPvB), and it carries a harmonised classification as suspected of damaging fertility. The EU has also listed it as an endocrine disruptor, though that classification is scientifically contested.
How does it differ from D5?
They are close siblings and behave similarly in the bedroom — both are volatile silicones that evaporate off skin and hair into the air. The differences are in degree and concern: D4 is present at lower levels in products (D5 is the dominant one), but D4 draws more regulatory concern because, unlike D5, it shows reproductive and weak estrogenic effects in animal studies and is a suspected fertility toxicant. So D4 is the smaller-but-more-restricted of the two.
Should I be worried about it?
For everyday airborne exposure, the human-health concern is modest and centers on reproduction rather than cancer, and D4 is already being removed from cosmetics under EU rules. The strongest reasons to reduce it are environmental persistence and the precaution around fertility. The practical steps are the same as for D5: fewer silicone-heavy hair and skin products and good ventilation; product reformulation is steadily lowering it regardless.
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.