Simethicone
Simethicone is an anti-foaming silicone rated Clear; the only comedogenicity number it carries is a 1 from a single 1989 rabbit-ear assay, a score that assay's own author placed in the band he called "not considered significant."
Silicone (dimethicone + silica); breathable and non-comedogenic.
What it is
A defoamer. Chemically it is a mixture of dimethicone — polydimethylsiloxane — and a small fraction of silica; industry references describe that silica as hydrated and the blend as roughly nine parts dimethicone to one part silica, but chain length and ratio are grade-dependent, and the paper that scored this material records neither. Its CAS number is 8050-81-5. It is not an oil and not a fat, and it carries no fatty acids. In a cosmetic its job is narrow and mechanical: it lowers surface tension and collapses the bubbles and foam that form while a product is mixed and filled, so it appears low on an ingredient list and at small amounts. Its most familiar use is outside skincare altogether — it is the active ingredient in many over-the-counter anti-gas medicines, where the same anti-foaming action breaks up gas bubbles in the gut. Because it is mostly dimethicone, it is often written about as though it were dimethicone. It is not the same material, and the evidence for one is not the evidence for the other.
Why we rate it Clear
We rate it Clear at Low confidence, and the confidence is Low because there is exactly one relevant measurement in the corpus and it is a rabbit's ear. Simethicone was tested in the same 1989 assay that is the source of most of the comedogenic numbers in circulation. Fulton diluted ingredients to roughly 10% in propylene glycol, applied them to the inner ear of New Zealand albino rabbits, three rabbits per assay, five days a week for two weeks, and measured the width of the follicular keratosis. The silicones block of his table holds three rows: simethicone 1, dimethicone 1, and cyclomethicone 0, on his 0-to-5 scale. There is an exact row printed "Simethicone" — the 1 belongs to this material's name, not a neighbour's, which is not something that can be said of every score on this site. One thing about that 1 is worth stating plainly. It sits in the band Fulton's own key describes as "a minimal grade of 0 to 1 is not considered significant" — a non-finding, rather than a clean bill of health earned against a hard test. That is the whole of the measured record we could trace: one legacy rabbit assay, one investigator, one score at the bottom of the scale. Fulton records no supplier and no composition for his simethicone sample, so which dimethicone grade it held, and how much silica, is not recoverable from the paper. So the reading that survives is modest. Simethicone was scored once, by a single rabbit-ear study, at the cleanest end of its scale. That is a reasonable basis for Clear. It is not a basis for Moderate or High, and we do not reach for either — one legacy assay is not a body of evidence agreeing with itself.
What the evidence doesn’t tell you
We identified no human comedogenicity study of simethicone: none in a rabbit beyond Fulton's single row, none on a person, and none looking inside a follicle. The other legacy tables we hold do not carry it — Fulton's earlier 1984 rabbit-ear paper has no simethicone row, Morris and Kwan's 1983 survey has none, and Nguyen, Dang and Maibach's 2007 study does not list it among its test materials. Those three absences are verified against the papers themselves. The one number we do have descends from a 1989 rabbit-ear assay — three animals, a fortnight, follicular keratosis read under a micrometer — and that is not a face. The method is contested in the same way it is everywhere else on this site: Draelos and DiNardo (2006) found that ingredient scores from the rabbit assay do not reliably transfer to human skin, and a 2025 review in JAAD Reviews found that no standardised comedogenicity test exists at all and that the label "non-comedogenic" is unregulated. Those objections weaken any single legacy number, in either direction. The claim the reader most often meets — that silicones form a film that suffocates the skin and traps sebum and bacteria in the pore — is, as far as we can find, untested for simethicone specifically. Unproven is not the same as disproven, and that cuts in the reassuring direction here as much as it cuts against the alarming one. Two points about identity. Simethicone is a blend, not a single molecule, and Fulton discloses no composition for his sample, so the ratio of dimethicone to silica behind his 1 is unknown. And because it is mostly dimethicone, it is tempting to read dimethicone's separate evidence onto it — but a study of dimethicone is a study of dimethicone, and simethicone was scored on its own row. Finally, a restriction that is sometimes offered as evidence and is not: the European Union is phasing the cyclic siloxanes D4, D5 and D6 out of cosmetics on environmental grounds. Simethicone is a linear dimethicone plus silica, not one of those cyclic substances, and that restriction is neither a skin-safety nor a comedogenicity finding.
Where you’ll see it
On a label it appears as Simethicone, usually low on the ingredient list, because it does its job at small amounts. It turns up as a defoamer in cleansers, creams and lotions, sunscreens, colour cosmetics and hair products. Its best-known use is not in skincare at all: it is the active ingredient in many over-the-counter anti-gas remedies. Related silicones you will meet nearby — dimethicone, cyclopentasiloxane and cyclomethicone — are different materials with different data behind them, and the evidence on this page does not carry over 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 only comedogenicity data we hold for this material, and the source of most of the scores this site distrusts elsewhere. 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. The relevant row sits in the table's silicones block and reads "Simethicone 1" on the 0-to-5 scale — an exact name match, with no range, no asterisk and no parenthetical. Fulton gives no supplier or composition for the sample. His key puts 0 to 1 in the band "not considered significant". A single legacy rabbit assay by one investigator, cited as exactly that.
- Cosmetics Info (Personal Care Products Council) — ingredient profile, Simethicone An industry ingredient database, cited only for identity and function, not for comedogenicity. It records what simethicone is — a mixture of dimethicone and hydrated silica used as an anti-foaming agent and skin-conditioning ingredient — and it is the source of the approximate composition given on this page (roughly 90% dimethicone, 10% silica; CAS 8050-81-5), which is a description of the material in general and not of Fulton's sample. It makes no claim about pores, and no number on this page comes from it.
- Draelos ZD, DiNardo JC. "A re-evaluation of the comedogenicity concept." J Am Acad Dermatol 54:507-512 (2006) A peer-reviewed critique of the rabbit-ear method. It tested finished cosmetic products on small human upper-back panels and found that formulas can test non-comedogenic despite containing ingredients the rabbit assay had scored. It reports no per-ingredient score, and none is taken from it here; it is cited for the caveat it actually establishes — that a single-ingredient rabbit number is a poor guide to a finished product on human skin — which cuts against leaning hard on Fulton's 1.
- "Comedogenicity in cosmeceuticals: a review of clinical relevance, regulatory gaps, and future directions." JAAD Reviews (2025) A recent peer-reviewed review of the whole field, covering literature from 1972 to 2025. It finds that no standardised comedogenicity test exists and that "non-comedogenic" is an unregulated label. A synthesis of the legacy literature rather than a new measurement, independent of Fulton only in authorship, since the corpus it surveys includes his. Cited for the field-wide caveat that any single legacy score, including this one, should be read against.
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 2026-08-12 · How we decide