Cyclotetrasiloxane (D4, CAS: 556-67-2), Cyclopentasiloxane (D5, CAS: 541-02-6) and Cyclohexasiloxane(D6, CAS: 540-97-6) are cyclic siloxanes used in cosmetic formulations, particularly to improve spreadability, lightness and the silky sensory profile of products.
Commission Regulation (EU) 2024/1328 amends Annex XVII to Regulation (EC) No 1907/2006, known as REACH, introducing new restrictions on D4, D5 and D6. Although the regulation concerns REACH rather than the Cosmetics Regulation directly, it has a significant impact on cosmetic products, especially leave-on products containing Cyclopentasiloxane or Cyclohexasiloxane.
The restrictions are mainly based on environmental concerns.
D4, D5 and D6 have been identified as substances of very high concern due to their persistence and bioaccumulative properties in the environment.
In particular:
- D4 – Cyclotetrasiloxane has been identified as a persistent, bioaccumulative and toxic substance (PBT) and as a very persistent and very bioaccumulative substance (vPvB);
- D5 – Cyclopentasiloxane and D6 – Cyclohexasiloxane have been identified as vPvB substances and, where they contain D4 at a concentration equal to or above 0.1% by weight, also as PBT substances.
The Regulation states that widespread uses in cosmetic products represent a major source of environmental release. The aim of the restriction is therefore to reduce emissions of these cyclic siloxanes during the life cycle of products.
What Does Regulation (EU) 2024/1328 Provide?
As a general rule, D4, D5 and D6 may not be placed on the market:
- as substances on their own;
- as constituents of other substances;
- in mixtures;
where the concentration of the respective substance is equal to or greater than 0.1% by weight.
Specific application dates apply to cosmetic products, depending on the substance and the type of product concerned:
Cyclotetrasiloxane / D4 is already prohibited in cosmetic products under Annex II/1388 to Regulation (EC) No 1223/2009
Cyclopentasiloxane / D5 may not be placed on the market in cosmetic products other than rinse-off products at a concentration equal to or above 0.1% by weight after 6 June 2027
Cyclohexasiloxane / D6 may not be placed on the market in cosmetic products at a concentration equal to or above 0.1% by weight after 6 June 2027
Products requiring particular attention may include:
- face serums and leave-on treatments;
- primers, foundations and other make-up products;
- hair leave-on products;
- body oils and lightweight fluids;
- deodorants;
- sprays and aerosol products;
- rinse-off products containing Cyclohexasiloxane.
Attention: Cyclomethicone may refer to a mixture of volatile cyclic siloxanes, which can include D4, D5 and D6 in varying proportions. The European Commission’s SCCS has described Cyclomethicone as a term covering cyclic siloxanes including Cyclotetrasiloxane, Cyclopentasiloxane and Cyclohexasiloxane.
Therefore, where Cyclomethicone appears in a formula or in raw material documentation, the supplier should be asked to confirm the possible presence and concentration of D4, D5 and D6.
