Dimethicone
Dimethicone is accused of forming a plastic film that suffocates skin and traps bacteria in the pore; the one human trial to go looking found silicone films are permeable to water vapour and behave nothing like an occlusive, and no study we could find has ever tested the trapping claim at all.
Breathable silicone; broadly regarded as non-comedogenic.
What it is
A silicone. Chemically it is polydimethylsiloxane, a chain of alternating silicon and oxygen atoms with methyl groups hanging off the silicon. It is not an oil and not a fat; it has no fatty acids in it, which already puts it outside the chemical class Fulton found most capable of plugging a follicle. Formulators use it for feel and for film. It spreads thin, fills in surface texture, and leaves a dry silky slip rather than a greasy one, which is why it sits behind most primers, most "blurring" claims, and a large share of mainstream moisturisers. Cosmetic dimethicone is not one substance but a family of chain lengths sold by viscosity, from thin fluids to gums. The Cosmetic Ingredient Review reports it in 12,934 products as of 2019, at concentrations up to 85% in dermal-contact products.
Why we rate it Clear
We rate it Clear at Moderate confidence. The evidence is thinner than the confidence of the internet on either side of this argument, so it is worth setting out exactly. Dimethicone was tested in the same 1989 rabbit-ear assay that produced almost every comedogenic number online. Fulton diluted ingredients to roughly 10% in propylene glycol and applied them to the inner ear of New Zealand albino rabbits, three rabbits per assay, for two weeks, then measured the width of the follicular keratosis. Section VIII of his table is "Silicones", and it contains simethicone, dimethicone and cyclomethicone. His verdict in the text is one sentence long: "The silicones and sterols do not appear to be a problem." The score of 1 that circulates on ingredient lists sits inside the band Fulton himself described as "a minimal grade of 0 to 1 is not considered significant." That is the same assay we distrust everywhere else on this site, and it is not what raises our confidence. Two other things do. The first is mechanism, from Fulton's own paper: he proposed that to be comedogenic a molecule must penetrate the follicle, and that the ingredients with the most potential have a molecular weight between roughly 200 and 300 and an HLB around 10 to 12. A silicone polymer is far outside both. The CIR Expert Panel reached the same structural conclusion from the toxicology side, judging it unlikely that these polymers are absorbed into skin at all given their large molecular weights. The second is a human study, and we have to be careful about what it does and does not show — because we were not careful enough, and an external fact-check caught it. De Paepe and colleagues (Skin Pharmacology and Physiology, 2014) applied three common silicone excipients, three creams containing 10% of those silicones, and petrolatum to the forearms of 26 healthy young women in a randomised comparison, then tracked transepidermal water loss and skin hydration over time. Petrolatum behaved like an occlusive: it formed a layer and drove skin hydration up for more than four hours. The silicones did not. Both reduced water loss at 15 minutes, but the silicone readings were not statistically distinguishable from untreated skin, and the authors call the idea that silicone excipients are occlusive substances blocking water loss a misconception, in that word. What that study measured is water leaving the skin. It did not look inside a follicle. It did not count a comedone, did not measure whether anything was trapped in a pore, and did not test a face. We previously wrote that it was "designed to test the claim, and the claim did not survive it." That is more than the paper earns. The pore-clogging story about dimethicone has two links — silicone forms an occlusive film, and that film traps sebum and bacteria in the follicle — and De Paepe cuts the FIRST link, on the forearm, by a proxy measurement. It says nothing whatsoever about the second. Nobody we can find has tested the second. So the rating rests on this: a rabbit-ear assay we take with the same salt as everywhere else, a mechanistic argument, a toxicological structural argument, and one human study that undermines the first half of the proposed mechanism without ever going near the second. That is a reasonable basis for Clear. It is nowhere near a basis for High, and the fact that the myth is unproven is not the same as the myth being disproven.
What the evidence doesn’t tell you
We can find no human study testing whether dimethicone causes comedones. Not one. Every claim on this page in dimethicone's favour is either an argument from structure, a rabbit's ear, or a measurement of water vapour, and none of those is a face. The 2006 re-evaluation by Draelos and DiNardo in the Journal of the American Academy of Dermatology found that rabbit-ear results do not reliably transfer to human skin, and the 2025 JAAD Reviews survey of the field found that no standardised comedogenicity test exists and that "non-comedogenic" is an unregulated label. Those papers cut in both directions. They are the reason we do not trust the 4 that every list prints for coconut oil — a number Fulton never actually assigned it — and they are equally the reason we cannot lean hard on dimethicone's 1. The specific claim that a silicone film traps bacteria, sebum and debris inside the follicle is, as far as we can find, untested. We could locate no published study that measured it. That is not the same as the claim being false; it means the people repeating it are not repeating a finding. The De Paepe trial is also narrower than it is usually made to sound: 26 young women, forearm skin, a single application, effects measured over hours. It says a silicone film lets water vapour through. It says nothing about a face after eight weeks of daily use, and it did not count a single comedone. Two further gaps. "Dimethicone" on a label does not specify chain length or viscosity, and neither Fulton nor the CIR distinguished between them, so the evidence is thinner than the single word implies. And the assays test an ingredient, not a formula; dimethicone is almost never the only thing in the product, and a product can break someone out for reasons that have nothing to do with the ingredient they blamed. Finally, a distinction that gets deliberately blurred. The European Union has restricted the cyclic siloxanes D4, D5 and D6 in cosmetics under Commission Regulation (EU) 2024/1328. That restriction exists because those substances are persistent and bioaccumulative in the environment. It is not a skin-safety finding, it has nothing to do with pores, and dimethicone, a linear polymer, is not one of the restricted substances. Anyone offering the siloxane restriction as evidence that dimethicone clogs pores is changing the subject.
Where you’ll see it
Primers, mattifying and "blurring" products, foundations, sunscreens, hair serums, shaving products, and a large proportion of ordinary facial moisturisers, including many marketed to acne-prone skin. It appears on labels simply as Dimethicone, usually in the top third of the ingredient list. Related entries you will meet nearby include dimethicone crosspolymer, cyclomethicone, cyclopentasiloxane and dimethiconol; they are different molecules with different data behind them, and the evidence on this page is not transferable to them.
Sources
Each source says what it actually is. Several widely-cited “sources” for comedogenic ratings are republishing the same 1989 assay, and counting them as independent agreement is how a thin evidence base gets made to look thick.
- Fulton JE. "Comedogenicity and irritancy of commonly used ingredients in skin care products." J Soc Cosmet Chem 40:321-333 (1989) The primary source, and the only assay in the corpus we searched that actually tested dimethicone for comedogenicity. Method: ingredient diluted to roughly 10% in propylene glycol, applied to the inner ear of New Zealand albino rabbits, three rabbits per assay, five days a week for two weeks, follicular keratosis measured with a micrometer. Dimethicone appears among the silicone rows of his table. Our transcription records section headings for two blocks of that paper only, and this is not one of them, so we give the row rather than a heading we cannot produce. The same paper is where the ratings we distrust for other ingredients come from, and it is also where the molecular-weight and HLB argument in its favour comes from. Both things are true.
- De Paepe K, Sieg A, Le Meur M, Rogiers V. "Silicones as nonocclusive topical agents." Skin Pharmacol Physiol 27(3):164-171 (2014) The load-bearing source on this page, and the closest thing to a direct test of the myth. A randomised comparative human trial: three silicone excipients, three creams containing 10% silicone, and petrolatum applied to the forearms of 26 healthy young female volunteers, with transepidermal water loss and hydration measured over time. Petrolatum was occlusive and raised skin hydration for over four hours; the silicones were not statistically different from untreated skin. The paper explicitly names the belief that silicone excipients block water loss as a misconception. Independent of Fulton. It did not measure comedones.
- Bian P, Wang Y, McCarthy TJ. "Rediscovering Silicones: The Anomalous Water Permeability of 'Hydrophobic' PDMS." Macromol Rapid Commun 42:2000682 (2021) Materials science on the bench, not skin. Peer-reviewed measurement showing that cross-linked polydimethylsiloxane is simultaneously water-repellent and highly permeable to water vapour. Cited to establish the physical property, which is the reason the De Paepe result is not a surprise. It says nothing about skin, pores or acne, and is not offered as if it did.
- Draelos ZD, DiNardo JC. "A re-evaluation of the comedogenicity concept." J Am Acad Dermatol (2006) Peer-reviewed rebuttal of the rabbit-ear assay. Argues that its results do not reliably predict comedogenicity in human skin and that testing an isolated ingredient says little about a finished formula. Cited here against our own position as much as for it: it is why we will not raise confidence above Moderate on the strength of Fulton finding silicones unproblematic.
- "Comedogenicity in cosmeceuticals: A review of clinical relevance, regulatory gaps, and future directions." JAAD Reviews (2025) Recent peer-reviewed review of the whole field, covering literature from 1972 to 2025. Finds that no standardised comedogenicity test exists and that the "non-comedogenic" label is unregulated. It is a synthesis of the legacy literature, not a new measurement, and independent of Fulton only in authorship, since the corpus it surveys includes his.
- Cosmetic Ingredient Review. "Amended Safety Assessment of Dimethicone, Methicone, and Substituted-Methicone Polymers" (re-review, 2020; original final report 2003) Industry-funded but independently paneled toxicological safety review. Concluded these ingredients are safe as used, on the reasoning that the polymers are unlikely to be absorbed into skin given their large molecular weights. Also the source of the usage figures on this page: 12,934 reported uses of dimethicone in 2019, at maximum concentrations up to 85% in dermal-contact products. Important caveat, and the reason it is listed low: the CIR assessed systemic and irritation safety. It did not assess comedogenicity at all. It is evidence about penetration, not about pores.
- Commission Regulation (EU) 2024/1328, restricting D4, D5 and D6 cyclic siloxanes Cited to draw a line, not to support a claim. This is the EU restriction routinely offered as proof that "silicones are bad". It restricts the cyclic volatile siloxanes D4, D5 and D6 on the grounds that they are persistent and bioaccumulative in the environment. Dimethicone, a linear polymer, is not among the restricted substances, and the restriction is not a finding about skin, follicles or acne. An environmental-persistence argument is a real argument; it is simply a different one.
- CosDNA ingredient database The source currently attached to this ingredient in our own ratings file, and a republisher of the Fulton-derived scores. Not an independent measurement. The same is true of acne.org, Face Reality, Banish and Sofie Pavitt: on this ingredient, as on every other, they are not several sources agreeing but one 1989 assay quoted several times.
Others in the same family
Silicones behave similarly enough that the evidence for one is often wrongly read across to the others. These are its structural relatives, not a guess.
Last reviewed 2026-07-13 · How we decide