Cyclosiloxanes are often referred to as cyclotetrasiloxane (D4) and cyclopentasiloxane (D5) because of their antistatic, emollient, moisturizing, solvent, viscosity-controlling, and hair-conditioning properties in cosmetics.
However, concerns have been raised about its toxicity and environmental impact, and cyclotetrasiloxane (D4) is now recognized to be toxic to the human reproductive system.
It also accumulates in the environment, causing unpredictable long-term effects.
Cyclopentasiloxane (D5) may also be harmful to the environment and the European Commission published an update in January 2018 amending Annex XVII of REACH Regulation (EC) No 1907/2006.
After January 31, 2020, the concentration of D4/D5 in cosmetic products placed on the market and rinsed off after application should be less than 0.1% by weight of both substances. This has now been modified to include cyclohexasiloxane (D6) and it is expected that the restriction will be extended to include leave-on products.
