Cyclopentasiloxane

What it is

Cyclopentasiloxane, usually shortened to D5, is a cyclic silicone made of five silicon-oxygen units in a ring. It is a light, fast-evaporating fluid that carries other ingredients across the skin and leaves a dry, silky feel. The EU has progressively restricted it, not because of a skin-safety problem, but because it is very persistent in the environment and accumulates in aquatic life.

What it does well

• Gives an immediate silky glide that disappears without residue

  Its volatility is the whole point: it thins the formula for easy spreading, then evaporates, which is why it dominated primers and light creams before the restriction.

  Strong evidence

• Skin safety was assessed as acceptable by the EU scientific committee

  The SCCS concluded in its 2015 opinion that D5 in cosmetic products is safe at the reported use concentrations, with reservations for inhalable formats such as hair styling aerosols and sun care sprays. The restriction that followed came from environmental persistence, assessed under REACH, not from skin toxicity.

  Moderate evidence

Worth knowing

• Restricted in the EU for environmental reasons

  D5 is classed as very persistent and very bioaccumulative. Under REACH Annex XVII entry 70 it may not be placed on the EU market in wash-off cosmetics at 0.1% or more (since 31 January 2020), and Regulation (EU) 2024/1328 extended the same 0.1% cap to leave-on cosmetics from 6 June 2026. In practice this ends its use as a functional ingredient in EU cosmetics.

  Matters most toAnyone comparing EU and non-EU product formulas, and anyone who cares about the environmental footprint of their skincare.

• May carry traces of D4

  The SCCS noted that D5 raw material can contain traces of D4, which is classified as toxic to reproduction and is prohibited in EU cosmetics; suppliers are expected to minimise it.

  Matters most toRelevant to raw-material quality rather than to consumers directly.

Where the EU stands

Sources (2)

Every link goes to the original: a journal, a PubMed record or an EU document.

1. [1]
   Opinion on decamethylcyclopentasiloxane (cyclopentasiloxane, D5) in cosmetic products

   SCCS (Scientific Committee on Consumer Safety), European Commission, SCCS/1549/15 · 2015

   The SCCS concluded that D5 is safe in cosmetic products at reported concentrations, except in hair styling aerosols and sun care sprays where inhalation exposure could be excessive.

2. [2]
   A comparison between silicone-free and silicone-based emulsions: Technological features and in vivo evaluation

   International Journal of Cosmetic Science · 2022 · doi:10.1111/ics.12800

   Silicone-based emulsions did not occlude the skin or cause irritation, and were preferred by users for sensory feel.