Cyclomethicone
Cyclomethicone is not a single silicone but a mixture of low molecular weight volatile cyclic siloxanes, principally octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), and dodecamethylcyclohexasiloxane (D6) in varying proportions. All silicones in the mixture are volatile, meaning they evaporate from the skin or hair rather than remain on it. It functions as an emollient, hair conditioning agent, skin conditioning agent, and solvent. Its CAS numbers include 69430-24-6, 556-67-2, 541-02-6, and 540-97-6.
Cyclomethicone imparts a light skin feel with none-to-minimal after-feel due to its volatile nature. It makes formulas easy to spread and provides emollient properties. It conditions both skin and hair without leaving a heavy residue.
The SCCS has issued opinions on components D4 (Opinion 0893/05) and D4/D5 (Opinion 1241/10), indicating regulatory scrutiny of these cyclic siloxane components.
