Cyclomethicone
Also known as Cyclic methylpolysiloxane, Cyclic silicone blend, D4/D5/D6 blend
“CIR Expert Panel says: safe as used in cosmetics.”
Cyclomethicone is a generic INCI name for a commercial blend of cyclic methylpolysiloxanes — principally D4 (cyclotetrasiloxane, CAS 556-67-2), D5 (cyclopentasiloxane, CAS 541-02-6), and D6 (cyclohexasiloxane, CAS 540-97-6) — in varying proportions. The CIR Expert Panel assessed the full family in its 2011 group report (IJT 30(S3):149-227) and found all members safe as currently used in cosmetics, with minimal percutaneous absorption and no irritation or sensitization concern; the QRT row for CYCLOMETHICONE is Finding=S with no detail conditions. Critical EU caveat: the blend's components carry severe EU restrictions that CIR does not reflect — D4 is prohibited in EU cosmetics (Annex II, Regulation (EU) 2019/831) due to its CMR cat. 2 (reproductive toxin) classification under REACH; D5 and D6 are restricted to <0.1% in rinse-off products (Regulation (EU) 2018/35, effective 2020-01-31) and leave-on products (extended restriction, effective 2026-06-06). Because the INCI 'CYCLOMETHICONE' does not specify which cyclic siloxane(s) are present, any product declaring this INCI in an EU market should be presumed non-compliant if D4 or D5 ≥0.1% is present.
Lightweight volatile emollient; evaporates from skin without residue, imparting a silky, non-greasy feel
Excellent carrier for active ingredients and other silicones; improves spreadability
CIR Expert Panel found all cyclic siloxane members (D4/D5/D6/D7 and cyclomethicone) safe in current cosmetic practices:149-227, 2011)
Minimal dermal penetration at typical cosmetic use levels
- · D4 (cyclotetrasiloxane, CAS 556-67-2) — classified CMR cat. 2 (toxic to reproduction) in EU; prohibited in EU cosmetics under Annex II per Regulation (EU) 2019/831
- · CYCLOMETHICONE does not specify which cyclic siloxane(s) are present — EU compliance is indeterminate without compositional disclosure
- · Environmental persistence and bioaccumulation in aquatic organisms (PBT/vPvB criteria under REACH) — primary driver of EU restriction, not human dermal toxicity
- · Many formulators have replaced cyclomethicone with single-component D5 or D6 to allow compositional attestation; INCI 'CYCLOMETHICONE' on labels is increasingly rare in EU-compliant products
D5 (cyclopentasiloxane, CAS 541-02-6) and D6 (cyclohexasiloxane, CAS 540-97-6) — restricted to <0.1% in EU rinse-off cosmetics (Regulation (EU) 2018/35, effective 2020-01-31); extended restriction for leave-on products effective 2026-06-06
CIR Quick Reference Table (12/2017, revised 07/2018) — CYCLOMETHICONE row: Finding=S, Citation=JACT 10(1):9-19, 1991 (original report); I…
“Cyclomethicone | S | | JACT 10(1):9-19, 1991 (original report); IJT 30(S3):149-227, 2011”— QRT-122017revised072018.pdf, p. 40