Is Cyclopentasiloxane Safe? A Simple Answer You Can Trust

No, Cyclopentasiloxane is not an ingredient I accept in skincare. It’s a volatile silicone that gives products their silky, fast-drying feel. On skin it behaves well, with no allergy, no irritation, and under 0.1% absorbed. The trouble starts once it evaporates. It persists in the environment for decades, and Europe is removing it from cosmetics. I rate it Not A Fan.

Cyclopentasiloxane is being phased out of European cosmetics, not merely limited. Wash-off products lost it in January 2020, and every other cosmetic follows on June 6, 2027. Europe listed it in 2018 as a Substance of Very High Concern, calling it persistent, bioaccumulative and toxic. The United States and Canada set no limit at all.

Three answers below repay the read. First, why this silicone is nothing like the dimethicone in your foundation. Second, what Europe’s own safety panel refused to approve. Third, the one silicone I still allow and where.

What Is Cyclopentasiloxane?

Cyclopentasiloxane is a laboratory-made cyclic silicone, known to chemists as D5. The name describes its shape: five silicon units joined in a closed ring. That ring structure is what makes it different from every other silicone on a label.

Cyclopentasiloxane is volatile, meaning it evaporates at room temperature. Spread it on skin and most of it lifts away within minutes, leaving a smooth, dry finish and no greasiness. Formulators love it for exactly that disappearing act.

Its cousins share the pattern and the ring size gives each its name. D4 is Cyclotetrasiloxane, D6 is Cyclohexasiloxane, and older labels group them as Cyclomethicone.

What Does Cyclopentasiloxane Do In Cosmetics?

Cyclopentasiloxane carries other ingredients and then leaves. As a solvent it spreads pigments and actives evenly, and as an emollient it delivers slip without weight. Hair serums rely on it to smooth strands without greasing them.

Industry data recorded it in 2,459 products, more than any other cyclic silicone, at concentrations ranging from 0.0001% to 93%. That upper figure is not a typo. Some products were almost entirely this ingredient.

You’ll find Cyclopentasiloxane most often in:

• hair serums and anti-frizz products
• primers and foundations
• deodorants and antiperspirants
• sunscreens and sprays
• facial moisturizers
• cleansing balms and makeup removers
• hair styling sprays

Cyclopentasiloxane has no food use anywhere. The U.S. Food and Drug Administration (FDA) lists no approved food application, and Europe assigns it no E number.

Are All Silicones The Same?

No, and this is the most useful thing on the page. Silicones split into two groups that behave nothing alike, and one word on the label tells you which you have.

The cyclic silicones form closed rings and evaporate. Their names begin with cyclo: Cyclopentasiloxane, Cyclotetrasiloxane, Cyclohexasiloxane, Cyclomethicone. Because they evaporate, you breathe them, and because they resist breaking down, they persist once released.

The straight-chain silicones form long chains and stay put. Dimethicone is the familiar one, alongside larger versions like Dimethiconol. They sit on the skin surface, resist evaporation, and carry no Substance of Very High Concern listing.

The regulatory record confirms the split. Europe is phasing out the cyclic silicones D4, D5, and D6, while leaving Dimethicone untouched. Judging every silicone by one reputation gets this exactly backwards.

How Is Cyclopentasiloxane Made?

The route is straightforward silicone chemistry. Manufacturers hydrolyze a chemical called dimethyldichlorosilane, then separate the ring-shaped products by size. Nothing about the process resembles ethoxylation, so the concerns I raise about PEGs do not apply here.

Impurity is where it gets interesting. Europe’s safety panel states twice in one opinion that D5 “may contain traces of D4” which it classifies as toxic to reproduction.

The instruction that follows is remarkably soft. The panel says the D4 level “should be kept as low as possible,” without setting any number. A purity requirement with no figure attached is difficult to check and impossible to verify from a label.

Does Cyclopentasiloxane Penetrate The Skin?

Barely, and for an unusual reason: it leaves before it can. Rat testing measured about 0.09% of an applied dose absorbed, a tiny fraction by any standard.

Stranger still, the measured absorption falls over time. Europe’s review found the portion sitting in skin after 24 hours “migrated to the skin surface and continued to evaporate.” The skin releases it rather than taking it in.

That single fact reframes the whole ingredient. Skin penetration is the wrong question here, because what evaporates must go somewhere. Human volunteers who applied it showed raised levels in blood and exhaled breath.

What Is Cyclopentasiloxane Called On Labels?

Watch for these names:

• Cyclopentasiloxane
• D5
• Decamethylcyclopentasiloxane
• Cyclomethicone
• Cyclomethicone 5

Cyclomethicone deserves special attention, because it’s a mixture rather than a single ingredient. A product listing Cyclomethicone may contain D5, D4, D6, or a blend, and the label will not tell you which.

Does The U.S. FDA Restrict Cyclopentasiloxane In Food And Cosmetics?

No. Cyclopentasiloxane appears on no FDA list of prohibited or restricted cosmetic ingredients. No concentration limit applies in the United States.

The American review is also old and grouped. The industry safety panel cleared it in 2011 alongside D4, concluding the family safe as used. It has not revisited that conclusion since.

Two developments since have undercut it. Europe classified D4 as toxic to reproduction, then listed D5 as a Substance of Very High Concern. Both came after that American review closed.

Europe also starts from a different footing. Under its precautionary principle, regulators may move once evidence of harm becomes convincing.

EU Regulations About Cyclopentasiloxane

Europe has set a countdown rather than a limit. Commission Regulation (EU) 2024/1328 bars Cyclopentasiloxane at 0.1% or above from wash-off cosmetics, effective since January 31, 2020. Every remaining cosmetic falls under the same rule after June 6, 2027.

The grounds are environmental and unusually blunt. In June 2018, Europe added D5 to its list of Substances of Very High Concern. Two reasons were cited: persistent, bioaccumulative and toxic, plus very persistent and very bioaccumulative.

Europe’s safety panel had already declined to clear part of its use. Its 2015 opinion judged D5 safe at reported concentrations, with one exception: “hair styling aerosols and sun care spray products.”

The numbers behind that exception are worth seeing. A safety margin is the gap between the amount you actually breathe in and the amount scientists consider safe. Regulators want that gap to be at least 100 times, which builds in room for error.

Hair styling aerosol came out at 61 times, sun care aerosol at 68, and pump spray at 59. Counting all the products a person uses in a day together, the gap shrank to 43. Every one of those falls short of the cushion regulators ask for.

A further process is open. Europe has recommended D5 for its Authorization List, which would require special permission for any continued use.

Canadian Regulations About Cyclopentasiloxane

Canada restricts nothing here. Neither the Cosmetic Ingredient Hotlist nor Canada’s toxic substances list names Cyclopentasiloxane.

One neighbor on that list is telling. D4, the reproductive toxicant that rides along as an impurity, is itself named on Canada’s toxic substances list. The impurity is regulated while the ingredient carrying it is not.

Can Cyclopentasiloxane Cause Skin Allergy And Sensitization?

No, Cyclopentasiloxane does not cause skin allergy, and this is the strongest part of its record. The American safety panel found the data “do not suggest skin irritation or sensitization potential.”

Independent checks agree. The American Contact Dermatitis Society leaves every cyclic silicone off its core testing panel. Medical literature searches turn up no established allergy signal.

Credit where it belongs. If your only question is whether this ingredient will make your skin react, the answer is almost certainly no.

Is Cyclopentasiloxane A Hormone (Endocrine) Disruptor?

Not officially, and the picture has shifted since regulators last looked. No agency classifies D5 as a hormone disruptor, and Europe’s chemicals agency has never assessed it for hormone activity.

Newer animal work complicates that. A 2023 study gave D5 to female rats by mouth and reported more ovarian follicles, raised estradiol, and reduced progesterone. Its authors wrote that “the industry should reconsider using D5.”

A second 2023 study found raised estradiol and a shortened cycle in living animals. A laboratory dish test showed nothing. Both papers post-date every official review, which is why I treat the question as open.

Is Cyclopentasiloxane Safe To Use While Pregnant?

The direct evidence on D5 is reassuring. One-generation and two-generation rat studies found no significant effects on any parameter measured. Exposures reached 160 parts per million.

My caution lies with the passenger, not the ingredient. D5 may carry traces of D4, which Europe classifies as toxic to reproduction. No one has set a maximum for how much D4 is acceptable.

That unmeasured impurity is reason enough for me to skip it during pregnancy. If you are weighing a specific product, you should consult with your medical provider.

Are There Any Cancer Concerns Linked To Cyclopentasiloxane?

No agency classifies Cyclopentasiloxane as a carcinogen, and it appears on no cancer list in the United States or internationally. Genetic testing is clean: Europe’s panel concluded it has “no genotoxic potential.”

One animal finding still deserves a plain description. Rats breathing D5 for two years at the highest tested level developed more uterine cancers. The researchers themselves called that result unanticipated.

Industry argues the mechanism cannot happen in people, and that reading is contested in published comment. Notice the exposure route, though. The tumors came from breathing it, which is the route Europe’s panel also flagged for sprays.

Is Cyclopentasiloxane Bad For The Environment?

Yes, and this is the reason Europe acted. D5 is officially persistent, bioaccumulative and toxic. It’s also very persistent and very bioaccumulative, and those two findings drove its listing.

Those words carry specific meaning. Persistent means it resists breaking down for years. Bioaccumulative means it builds up in living things, moving up the food chain.

Consider where it goes. A silicone that evaporates off your skin enters the air, and what rinses down the drain resists treatment. This is the rare ingredient whose main problem starts after it leaves you.

Common Claims About Cyclopentasiloxane: What’s True And What’s Not

Claim: Cyclopentasiloxane Has No Side Effects

Half right, which is what makes this claim so durable. On skin the record genuinely is clean: no allergy, no irritation, no sensitization, and roughly 0.09% absorbed.

The claim quietly assumes side effects can only happen on skin. Europe refused to clear D5 in hair styling aerosols and sun care sprays. Breathing it produced air concentrations above the safe value, with combined exposure margins of 43.

Three more effects sit outside the skin. Rats breathing it for two years developed uterine tumors. Studies in 2023 found hormone changes, and Europe classifies it as persistent and bioaccumulative.

A fair sentence would be that Cyclopentasiloxane has few effects on skin. Saying it has no side effects requires ignoring inhalation, the environment, and every regulatory action of the past decade.

Claim: All Silicones Are The Same

This one is wrong in both directions, and it costs people twice. It leads some to avoid Dimethicone needlessly, and others to accept Cyclopentasiloxane because a gentler silicone earned trust.

The shape decides everything. Ring-shaped cyclic silicones evaporate, get breathed in, and persist in the environment. Chain-shaped silicones like Dimethicone stay on the skin, wash off, and carry no such listing.

Regulators treat them differently for that reason. Europe is removing D4, D5, and D6 from cosmetics while leaving Dimethicone alone. That is not a rounding error in policy.

The practical test takes one second. Look for the prefix cyclo at the start of the word. That single check separates the two families without any chemistry.

Claim: Silicones Suffocate The Skin

Not true of either type, and the physics says so. Silicone films are breathable, allowing water vapor and gases through, which is why dermatologists use silicone sheets on healing scars.

Cyclopentasiloxane could hardly suffocate anything, since most of it evaporates within minutes. My objections have nothing to do with pores or breathing skin.

What I Think About Cyclopentasiloxane — And What You Should Do

I rate Cyclopentasiloxane Not A Fan for skincare. I want to be precise about why, because the usual reasons do not apply here. Let me give it full credit first. It does not irritate, does not sensitize, barely absorbs, and shows no genotoxicity. Judged only by what happens on skin, it would rate well.

Three things about Cyclopentasiloxane decide its rating for me. First, Europe is removing it from cosmetics by June 2027, having named it persistent, bioaccumulative and toxic. Second, its own safety panel refused to clear sprays, where combined exposure margins fell to 43. The third is the impurity. D5 carries traces of a reproductive toxicant, and no purity limit has been set.

Here’s where I part company with people who avoid all silicones. I do accept Dimethicone in certain makeup products, because it does a job nothing natural does as well. It gives foundation its glide, keeps pigment from settling into lines, and helps makeup last without constant touching.

Skincare is different, and my answer there is no. A moisturizer is meant to feed skin, not coat it, and plant oils do that job beautifully. Silicone in skincare buys a texture I can get elsewhere.

Here’s the practical part. Scan for the prefix cyclo on any label and treat those five letters as your signal to skip the product. Hair serums and setting sprays hide D5 most often, and squalane or jojoba replace it comfortably.

Frequently Asked Questions About Cyclopentasiloxane

Is Cyclopentasiloxane Safe For Acne-Prone Skin?

Yes, on the pore question specifically. Cyclopentasiloxane is not comedogenic, and it evaporates within minutes of application, leaving little behind to block anything.

If breakouts follow a product containing it, look at the ingredients that stay. Heavy oils, waxes, and incomplete cleansing of long-wear makeup are the usual culprits, not the silicone that left.

Are Cyclopentasiloxane And Dimethicone The Same?

No, and the difference is the point of this post. Cyclopentasiloxane is a ring that evaporates. Dimethicone is a long chain that stays on the skin surface.

Their regulatory positions differ just as sharply. Europe is phasing Cyclopentasiloxane out of cosmetics as a Substance of Very High Concern, while Dimethicone faces no such action.

Are Cyclopentasiloxane And Cyclohexasiloxane The Same Substance?

No. They are neighbors in the same family, distinguished by ring size: Cyclopentasiloxane has five silicon units, Cyclohexasiloxane has six.

Europe treats them as one problem regardless. The 2024 restriction covers D4, D5, and D6 together, so swapping one for another solves nothing.

What Is The Difference Between Cyclopentasiloxane And Cyclomethicone?

Cyclopentasiloxane is one specific molecule. Cyclomethicone is a category name for a mixture of ring silicones, which may contain D4, D5, D6, or several together.

That vagueness matters now. A label saying Cyclomethicone tells you less than one naming D5. Older cyclomethicone blends contained substantial amounts of D4, the reproductive toxicant.

What Is A Natural Alternative To Cyclopentasiloxane?

Squalane is the closest match. Plant-derived squalane is light, dry-feeling, and spreads like a silicone without the ring structure or the persistence.

Others suit specific jobs. Jojoba oil mimics skin’s own sebum, and coco-caprylate gives silky slip in moisturizers. Isoamyl laurate brings the fast-absorbing feel that makes primers pleasant.

What Are Biodegradable Silicone Alternatives?

Several ingredients now target this precise gap. Coco-caprylate, isoamyl laurate, and heptyl undecylenate are plant-derived esters designed to replace volatile silicones, and they break down readily.

Check how they are made before you celebrate. Some silicone alternatives are ethoxylated, which trades one manufacturing concern for another. Simple plant esters avoid both.

Sources

EU SCCS / SCCP Opinions:

SCCS/1549/15, Opinion on decamethylcyclopentasiloxane (cyclopentasiloxane, D5) in cosmetic products, adopted 25 March 2015, final version 29 July 2016 (safe at reported concentrations except hair styling aerosols and sun care sprays; notes D5 may contain traces of D4): SCCS/1549/15

SCCS/1241/10, Opinion on Cyclomethicone (Octamethylcyclotetrasiloxane D4 and Decamethylcyclopentasiloxane D5), 2010 (the earlier group opinion): SCCS opinions portal

Cosmetic Ingredient Review (CIR) Reports:

Johnson W Jr, et al. (2011). Safety Assessment of Cyclomethicone, Cyclotetrasiloxane, Cyclopentasiloxane, Cyclohexasiloxane, and Cycloheptasiloxane. International Journal of Toxicology 30(Supplement 3) (the American conclusion, not revisited since): cir-reports.cir-safety.org

European Union Regulatory Databases:

CosIng entry for CYCLOPENTASILOXANE (no Annex entry); restricted under Commission Regulation (EU) 2024/1328, 0.1% limit applying to wash-off cosmetics from 31 January 2020 and all other cosmetics from 6 June 2027: EU CosIng database

ECHA Candidate List, Decamethylcyclopentasiloxane, EC 208-764-9, CAS 541-02-6, included 27 June 2018; reason for inclusion PBT (Article 57d) and vPvB (Article 57e): ECHA CHEM 100.007.969

REACH Annex XVII entry 70 (group restriction covering D4, D5 and D6); Annex XIV recommendation for the Authorization List remains ongoing: ECHA CHEM

Other Regulators:

U.S. FDA, Cyclopentasiloxane is not on the prohibited or restricted cosmetic ingredients list, and has no approved food use: FDA prohibited and restricted cosmetic ingredients

Health Canada Cosmetic Ingredient Hotlist (not listed, neither prohibited nor restricted): Cosmetic Ingredient Hotlist

Environment Canada CEPA Schedule 1, Cyclopentasiloxane not listed; Cyclotetrasiloxane (D4) is listed:  CEPA Schedule 1

IARC (not classified): IARC List of Classifications

U.S. NTP 15th Report on Carcinogens (not listed): NTP Report on Carcinogens

California Proposition 65 (not listed): OEHHA Proposition 65 list

PubChem Records (Chemistry, Identifiers, Skin Penetration, Hazard Codes):

Decamethylcyclopentasiloxane, CID 10913, molecular weight 370.77; made by hydrolysis of dimethyldichlorosilane; not classified under GHS in 97% of reports: PubChem CID 10913

Peer-Reviewed Studies:

Jean PA, Plotzke KP (2016). Chronic toxicity and oncogenicity of decamethylcyclopentasiloxane in the Fischer 344 rat. Regulatory Toxicology and Pharmacology 74(Suppl): S57-S66. PMID 26184430 (the uterine tumor finding): PubMed

Franzen A, et al. (2017). Toxicology and Industrial Health (argues the uterine tumor mechanism is not relevant to humans). PMID 28092229: PubMed

Endocrine effects of D5 in female rats (2023). Toxics 11(4): 302. PMID 37112528 (reports raised estradiol and altered follicle development): PubMed

D5 and estrous cyclicity (2023). Journal of Applied Toxicology 43(12): 1883-1898. PMID 37551828: PubMed

Natural Cosmetic Standards:

COSMOS-standard approved and certified raw materials (no result for cyclopentasiloxane): COSMOS-standard database

NATRUE certified and approved raw materials (no result for cyclopentasiloxane): NATRUE certified world

Skin Allergy Resource:

American Contact Dermatitis Society, Helpful References, including the Core Allergen Series 2020; no cyclic silicone appears on the core panel: ACDS Helpful References

Last verified: 09-01-2026