At a glance
| Chemical family | Cyclic volatile methylsiloxane (cVMS) — six-membered siloxane ring (D6) |
| CAS number | 540-97-6 |
| Classification | Not classified by IARC. EU SVHC candidate — identified as vPvB (very persistent, very bioaccumulative). REACH Annex XVII Entry 70 restricts D4, D5, and D6 in wash-off cosmetic products to 0.1% |
| Where you encounter it | Personal care products (leave-on cosmetics, deodorants); silicone polymer manufacture; industrial solvent; indoor air in homes and personal spaces |
| Sleep micro-environment relevance | Present in indoor air from personal care product use. Transfers to bedding from skin. Part of the cumulative siloxane exposure alongside D4 and D5 |
Regulatory & certification status
| European Union | SVHC candidate (vPvB). REACH Annex XVII Entry 70 restricts D4, D5, and D6 in wash-off cosmetic products to 0.1% (effective January 2020). Leave-on products not yet restricted. ECHA evaluating broader restriction. Regulatory — European Union authority |
| United States | No FDA restriction on D6 in cosmetics. EPA TSCA inventory listed. Not classified as a health hazard at consumer exposure levels. Regulatory |
| Canada | Environment and Climate Change Canada assessed siloxanes. D4 and D5 declared CEPA-toxic; D6 under related assessment. Regulatory |
| International | Not IARC classified. EU SVHC candidate (vPvB). REACH Entry 70 restricts all three (D4, D5, D6) in wash-off cosmetics. Regulatory |
What it is
D6 is a cyclic organosilicon compound consisting of six repeating dimethylsiloxane units arranged in a ring. Like its smaller analogues D4 and D5, it is a clear, odourless, volatile liquid with a silky skin feel — properties that make cyclic siloxanes valued in cosmetic formulations. D6 is used less widely than D5 in personal care products but is still present in some leave-on products and as a by-product of silicone polymer manufacture. IARC has not evaluated D6. The EU identified it as a vPvB substance alongside D4 and D5, and all three are restricted in wash-off cosmetic products (concentration limit 0.1%) under REACH Annex XVII Entry 70. D6 has endocrine-disrupting potential under investigation — some studies report weak estrogenic activity, similar to D4 and D5, but the evidence is less extensive than for its smaller analogues.
Where it shows up in bedding
D6 enters the bedroom through the same pathways as D4 and D5 — personal care products applied to skin before bed (deodorants, body lotions, hair products) release D6 into indoor air and transfer residues to pillowcases and sheets. Indoor air surveys consistently detect cyclic siloxanes in residential bedrooms, with D5 typically dominant and D6 present at lower but detectable concentrations. The high volatility of cyclic siloxanes means they evaporate from skin and textiles rapidly, contributing more to air exposure than to sustained skin contact. Ventilating bedrooms reduces airborne siloxane concentrations.
Citations
- ECHA. Dodecamethylcyclohexasiloxane (D6) — Substance Information. Source Regulatory
- Horii, Y. and Kannan, K. (2008). Survey of Organosilicone Compounds, Including Cyclic and Linear Siloxanes, in Personal-Care and Household Products. Archives of Environmental Contamination and Toxicology, 55(4): 701-710. Source Peer-reviewed
- EU Commission Regulation (EU) 2018/35 restricting D4, D5, and D6 in wash-off cosmetic products. Source Regulatory
Frequently asked questions
Is D6 more dangerous than D4 or D5?
D6 is identified as vPvB (very persistent, very bioaccumulative) by the EU, alongside D4 and D5. D4 has the additional concern of being classified as Repr. 2 (suspected reproductive toxicant). D6 has not been classified for reproductive toxicity. In terms of human exposure, D5 is typically the dominant cyclic siloxane in personal care products, with D6 present at lower concentrations.
Why are cyclic siloxanes restricted in wash-off products?
The EU restricted D4, D5, and D6 in wash-off cosmetics (shampoos, shower gels, liquid soaps) because these products are rinsed down the drain, releasing siloxanes into wastewater and eventually into the environment. Their vPvB properties mean they persist in the environment and accumulate in organisms. Leave-on products (lotions, deodorants) were not restricted because the siloxanes evaporate from skin rather than entering wastewater.
Related compounds
Embr is a sleep environment company researching and addressing the chemistry of the bedroom. Research and product development in progress.
Last reviewed 2026-07-08. If you find a factual error, contact us.