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Humectants & Emollients

Cyclopentasiloxane

Also known as: D5, Cyclomethicone D5, Decamethylcyclopentasiloxane

The silky-slip silicone — the secret behind 'velvety' textures, with an environmental-persistence debate attached.

  • By IngredientWiki Editorial Team
  • Fact-checked by IngredientWiki Editorial Team
  • Updated 2026-09-26
  • 2 min read

In short

Cyclopentasiloxane (D5) is a volatile silicone — a ring-shaped molecule that evaporates after application, leaving active ingredients deposited evenly on skin and a silky, non-greasy slip while it lasts. That unique behavior made it a backbone of primers, serums, hair oils, and antiperspirants. Its human safety record at cosmetic levels is strong: minimal irritation, no meaningful skin absorption, CIR-reviewed as safe. The debate around D5 is environmental — it is persistent and bioaccumulative in aquatic ecosystems, which is why the EU has restricted it in rinse-off products since 2020. The split mirrors zinc pyrithione's: cosmetic safety affirmed, environmental policy tightening.

  • Volatile silicone: evaporates after application
  • Creates silky, non-greasy product feel and even deposit
  • Human safety: excellent; minimal absorption
  • EU restricts rinse-off use (environmental persistence)

What is Cyclopentasiloxane?

Cyclopentasiloxane is the molecule behind the word 'velvety.' It is a volatile silicone that evaporates seconds after spreading, and in that brief life it does two valuable things: give formulas their silky, non-greasy glide, and carry actives into an even layer as it departs. That evaporation trick made D5 a primer, serum, and hair-product staple for three decades. The modern conversation around it is environmental, not dermatological — regulators restrict it in rinse-off products to protect aquatic ecosystems, even as its human-safety file remains clean.

Where it comes from

Natural sources

  • Fully synthetic cyclic silicone (five dimethylsiloxane units)
  • No natural occurrence; produced from silica via silicone chemistry

How it's made

Clear, odorless, volatile liquid; used at 1–50% in leave-on and rinse-off products.

What it does in products

  • Volatile carrier with silky slip
  • Even deposition of actives
  • Non-occlusive water resistance
  • Texture modification (anti-whitening, non-greasy feel)

Benefits

Superior skin feel

strong evidence

Provides the dry, silky glide that defines modern primers and serums — a sensory property that drives real consumer adherence to products.

Even active deposition

strong evidence

Evaporating D5 leaves actives uniformly distributed rather than pooled — the functional reason it appears in so many treatment products.

Excellent human safety record

strong evidence

Minimal irritation, negligible absorption, and decades of CIR-reviewed use support safety at cosmetic concentrations.

Side effects & safety

Eye stinging with heavy application (uncommon)Common to volatile silicones generally.

Safety considerations

  • Considered safe in cosmetics; negligible systemic exposure.
  • None.
  • Not for: None established

How it's used

In supplements

Not an oral ingredient.

In skincare

1–50% depending on product type; highest in primers and hair oils.

Regulatory status

  • Permitted cosmetic ingredient.
  • INCI name on cosmetic labels: Cyclopentasiloxane.
  • CIR-reviewed and found safe in cosmetics; EU restricts rinse-off use from 2020 (environmental).

Popular products containing Cyclopentasiloxane

  • Smashbox Photo Finish Primer — The classic D5-anchored primerSmashbox · Skincare
  • Moroccanoil Treatment — Silicone-based hair oilMoroccanoil · Skincare
  • Many anti-frizz serums and primers — Industry-standard volatile siliconeVarious · Skincare

Product names and brands are shown for reference and belong to their respective owners.

The evaporation trick

D5 has a low boiling point near body temperature, so it evaporates within minutes of application. During that window it thins the formula for even spreading; as it departs, it leaves actives uniformly on the surface. No residue, no greasiness — the physics of the 'weightless' feel.

The environmental debate

D5 is persistent and bioaccumulative in aquatic environments, which drove the EU's 2020 rinse-off restriction. Leave-on products (where evaporation prevents wash-off entry) remain permitted. Formulators have responded with lower-volatility alternatives, and 'silicone-free' has become a marketing category in its own right.

Frequently asked questions

Do silicones clog pores?

Cyclopentasiloxane is rated non-comedogenic and evaporates rather than lingering in pores. The 'silicones clog pores' claim is largely myth.

Is D5 banned in cosmetics?

In the EU, rinse-off use is restricted; leave-on use remains permitted. In the US, it is unrestricted and CIR-approved.

Why do primers rely on D5?

Its silky slip fills fine lines temporarily and creates the smooth canvas makeup adheres to — the entire primer category was built on this silicone behavior.

The bottom line

Cyclopentasiloxane is a cosmetically safe, functionally brilliant volatile silicone whose real conversation has moved from the bathroom to the environment.

References

  1. Cyclopentasiloxane — Cosmetic Ingredient Review. CIR. https://www.cir-safety.org/ingredients
  2. D4/D5 silicones: environmental assessment. European Chemicals Agency. https://echa.europa.eu/
  3. Silicones in personal care. PubMed Central. https://pubmed.ncbi.nlm.nih.gov/31540572/