What it is
Cyclopentasiloxane is a five-unit cyclic silicone (one of the cyclomethicones) built from a ring of repeating silicon-oxygen units. It is water-thin with low viscosity and high volatility, so rather than staying on the skin it spreads easily and then evaporates. In formulas it acts as an emollient, solvent, and carrier, imparting a silky, smooth, non-greasy slip and helping other ingredients spread evenly; it is often paired with non-volatile dimethicone.
Safety & warnings
On skin, cyclopentasiloxane is widely used and generally considered non-irritating and non-sensitizing, and its volatility means much of it evaporates rather than lingering. The main debate around it concerns environmental persistence and bioaccumulation rather than skin tolerability, which is why it has drawn regulatory attention in some regions. People who simply prefer to avoid silicones may wish to note its presence.
Origin & sourcing
Cyclopentasiloxane is a synthetic silicone. It is produced industrially from silicon-based precursors such as dimethyldichlorosilane through hydrolysis, with reaction conditions that yield the cyclic ring structure. It is not found in nature.
History
Cyclopentasiloxane belongs to the family of polydimethylsiloxane-based silicones developed for industrial and personal-care use, valued for their volatility and smooth sensory feel. In 2024 the European Union designated D5 a substance of very high concern based on persistent, bioaccumulative, and toxic properties, while an earlier 2011 Canadian assessment had concluded the substance did not pose a danger to the environment.
Questions everyone asks
Does cyclopentasiloxane stay on my skin?
Largely no. It is a volatile silicone that spreads and then evaporates, which is why it leaves a silky feel without a heavy or tacky residue.
What is it doing in a sunscreen?
It works as a lightweight emollient, solvent, and carrier, helping the product spread smoothly and improving the sensory feel of the formula.
Is cyclopentasiloxane the same as D5?
Yes. D5, or decamethylcyclopentasiloxane, is the same five-unit cyclic silicone, one of the cyclomethicones.