Cyclopentasiloxane
Also known as D5, Decamethylcyclopentasiloxane, Pentacyclomethicone, DC 245 Fluid
“CIR Expert Panel says: safe as used in cosmetics.”
Cyclopentasiloxane (D5; CAS 541-02-6) is a cyclic volatile methyl siloxane (cVMS) used as a lightweight emollient and carrier in hair and skin formulations. The CIR Expert Panel assessed D5 as part of the cyclic siloxane group (IJT 30(S3):149-227, 2011) and found it safe as used in cosmetics, with minimal percutaneous absorption due to rapid volatilization from the skin surface. The SCCS likewise concluded in SCCS/1241/10 (22 June 2010) that D5 does not pose a risk for human health when used in cosmetic products. Despite the human-safety clearance, D5 is subject to EU environmental restriction: Commission Regulation (EU) 2018/35 restricted D4 and D5 in rinse-off cosmetics at concentrations >=0.1% (effective 31 January 2020) based on PBT/vPvB criteria under REACH; an extended restriction covering leave-on products at >=0.1% was adopted in 2024 and takes effect 6 June 2026.
Lightweight volatile emollient and slip agent; evaporates cleanly without residue, imparting silky skin feel
CIR Expert Panel found safe as used in cosmetics based on minimal systemic absorption:149-227, 2011)
SCCS found no human health risk at in-use cosmetic concentrations (SCCS/1241/10, 22 June 2010)
Widely used in hair conditioners, antiperspirants, and skin primers as a volatilizing carrier
- · Trace D4 (cyclotetrasiloxane) impurity in commercial D5; D4 classified as reprotoxic category 3 (ECB 2006) in EU
- · Environmental persistence: D5 detected in aquatic environments and biota; identified as very persistent and very bioaccumulative (vPvB) by ECHA under REACH
EU REACH-based restriction: D5 banned in rinse-off cosmetics >=0.1% since 31 January 2020 (Commission Regulation EU 2018/35); extended restriction for leave-on products >=0.1% effective 6 June 2026 — driven by environmental persistence and bioaccumulation (PBT/vPvB), not human toxicity
CIR Quick Reference Table (12/2017, revised 07/2018) — Cyclopentasiloxane row: Finding=S, Citation=IJT 30(S3):149-227, 2011
“Cyclopentasiloxane | S | [no detail column entry] | IJT 30(S3):149-227, 2011”— QRT-122017revised072018.pdf, p. 40 (Cy section)
SCCS/1241/10 — Opinion on Cyclomethicone (D4, D5): Octamethylcyclotetrasiloxane and Decamethylcyclopentasiloxane, adopted 22 June 2010
“The SCCS is of the opinion that cyclomethicone (D4, D5) does not pose a risk for human health when used in cosmetic products. Other uses were not considered in this risk assessment.”— SCCS/1241/10, p. 102 (Section 4. Conclusion)