Cyclopentasiloxane (D5): Filing a Volatile Silicone

Silicones get a lot of unfair blame in clean-beauty marketing, but cyclopentasiloxane is genuinely one of the more scrutinized ones in the group, and not for vague reasons. It's worth understanding what it actually is before you decide whether it belongs in your formula and how to handle it on a filing.

What Cyclopentasiloxane Is

Cyclopentasiloxane, commonly abbreviated D5, is a cyclic volatile silicone. "Volatile" here means it evaporates readily from skin after application, which is exactly why formulators like it: it delivers a silky, non-greasy glide during application and then largely disappears, leaving behind a light, dry-touch finish rather than an occlusive film. That's the appeal in primers, some sunscreens' vehicle systems, hair serums, and antiperspirants.

Functionally, it's typically listed as a skin conditioning agent or solvent, depending on the formula's use of it.

INCI and CAS Basics

Detail	Value
INCI name	Cyclopentasiloxane
Common abbreviation	D5
CAS number	Confirm on your supplier's current safety data sheet, as silicone CAS registrations can vary by grade and source
Typical function	Skin conditioning agent, solvent, carrier
Typical use level	Varies widely by product type, from under 1 percent in a serum blend to a majority carrier in some primer formulas

Always pull the specific CAS number from your supplier's documentation rather than assuming a single universal number, since this is a case where sourcing and grade can matter.

The D4 Contamination Question

This is the detail that actually changes how you should treat D5 on a filing. D5 is manufactured through processes that can leave trace levels of D4, cyclotetrasiloxane, a related but distinct cyclic silicone that has drawn more regulatory attention in various markets due to environmental persistence and bioaccumulation concerns raised in some jurisdictions' assessments.

The practical implication: if you're sourcing D5, you want a supplier certificate of analysis that specifies the D4 trace level, not just a generic silicone purity statement. A batch of D5 with meaningfully higher D4 contamination is a different risk profile than a well-refined batch, even though both would be labeled identically as Cyclopentasiloxane on your ingredient list.

This is also a reminder that INCI naming identifies the primary substance, not trace contaminants. Your ingredient list correctly says Cyclopentasiloxane regardless of D4 trace levels, but your due diligence, your safety substantiation file, and your supplier vetting should go a layer deeper than the INCI name.

What to Check Before Sourcing

• Certificate of analysis with D4 specification. Ask directly, don't assume the standard CoA covers it.
• Safety data sheet section 3, which lists composition, should reflect the actual material you're buying, including any relevant impurity specifications the supplier discloses.
• Current restriction status in whichever markets you're selling into. Restriction and concern levels around cyclic silicones have shifted in some jurisdictions over time, so treat any specific limit as something to verify against the current Health Canada Cosmetic Ingredient Hotlist or the relevant market's current list, rather than something fixed permanently by an older reference.

Filing Notes

On a Cosmetic Notification Form, cyclopentasiloxane is declared like any other ingredient, by INCI name with its concentration or concentration range in the finished product. Where formulators sometimes stumble is in supplier blends: D5 often arrives as part of a premixed carrier system alongside other silicones like dimethicone or cyclohexasiloxane, and it's easy to report the blend's overall percentage without breaking out how much of that blend is actually D5 specifically versus its silicone siblings.

If your formula uses a silicone premix, get the component breakdown from the supplier and calculate D5's real finished-product concentration the same way you would for any other blended raw material, by multiplying the component percentage within the blend by the blend's use level in your formula.

The Bigger Picture

D5 isn't a banned or universally restricted ingredient, and plenty of well-formulated, compliant products use it. The work here is diligence, not avoidance: know your D4 trace level, verify current status against the Hotlist before you finalize a formula, and expand any silicone blend down to its real components before you file.

Cosmetic Comply matches ingredients like cyclopentasiloxane to their correct INCI name and CAS number, expands supplier blends into their real components and concentrations, and screens each one against the current Hotlist with a confidence score before a human reviewer signs off, which takes a fair amount of this guesswork off your desk.