Steareth-10
Steareth-10 is one of the ingredients whose circulating comedogenic number is a genuine measurement of the exact material: Fulton's 1989 rabbit-ear assay scored it 4, in the band he called positive. What the charts leave out is the rest of the column — the same table scores steareth-2 a 2, steareth-20 a 2 and steareth-100 a 0, so steareth-10 is the single highest-scoring member of its own series, and the number falls off on both sides of it.
Ethoxylated stearyl alcohol flagged comedogenic by acne-community lists.
What it is
Steareth-10 is a nonionic surfactant made by attaching a chain of, on average, ten ethylene-oxide units to stearyl alcohol — the eighteen-carbon saturated fatty alcohol that corresponds to stearic acid. On a label it is Steareth-10, and the "10" is that average number of ethylene-oxide units, not a fixed count. The Cosmetic Ingredient Review's 2012 assessment of the alkyl PEG ethers describes the steareths as surfactants and emulsifiers; the EU CosIng database lists steareth-10's functions as refatting, cleansing surfactant and emulsifying surfactant. In a formula it is usually the emulsifier that holds an oil phase and a water phase together, which is why it turns up in creams, lotions and emulsion cleansers. At ten ethylene-oxide units it is water-soluble rather than oil-soluble, which places it in the middle of its own family: the steareths run from steareth-2, a barely-ethoxylated oil-soluble material, up to steareth-100, which is effectively a PEG. Its close relatives on the same shelf are separate ingredients with their own scores, and the legacy table treats them very differently. Steareth-2, Steareth-20 and Steareth-100 are the same stearyl alcohol carrying fewer or more ethylene-oxide units, and each has its own row. Only steareth-10 carries the 4.
Why we rate it Clogging
We rate it Clogging, at Low confidence, and this page is unusual in the way the laureth-4 and oleth-3 pages are: the number is real. Most of the scores this site takes apart turn out to belong to a different material — a neighbouring row, a derivative, a dropped word. Steareth-10's does not. Fulton's 1989 table — the source of nearly every comedogenic number in circulation — prints Steareth-10 at 4 on his 0-to-5 scale. We read the row off a transcription of Table I rather than off a chart quoting it, and there is no ambiguity in it: the row is Steareth-10, not Steareth-2 (which he scores 2), not Steareth-20 (also 2), not Steareth-100 (0). It matters what a 4 is in Fulton's own words, because the charts that publish his numbers leave his key out: "a minimal grade of 0 to 1 is not considered significant. Grade 2 to 3 is borderline. However, a grade of 4 to 5 is uniformally reproduceable and considered positive." A 4 is in the positive band — not the borderline 2 to 3, and not the insignificant 0 to 1. So the rating is not a stretch from the evidence: the one three-rabbit experiment from one laboratory that we have puts this material in the range Fulton called positive, and we rate it Clogging to match. Now the thing the charts never print, and the reason this page exists. Read down Fulton's steareth rows in order of ethoxylation and they do not fall in a line: Steareth-2 scored 2, Steareth-10 scored 4, Steareth-20 scored 2, and Steareth-100 scored 0. The score rises to a peak at steareth-10 and then comes back down. This is different from his oleth series, which does fall cleanly as the molecule is ethoxylated further (Oleth-3 a 5, Oleth-5 a 3, Oleth-10 a 2, Oleth-20 a 1), and from his laureth pair (Laureth-4 a 5, Laureth-23 a 3). The tidy story people tell about these surfactants — that more ethylene oxide always means less clogging — is a real pattern in the oleth and laureth rows, and it is not what the steareth rows do: the least-ethoxylated steareth Fulton tested scored lower than steareth-10, not higher. We report this as a set of rows printed in one table, because that is all it is. It is not a law, and we are not going to supply a mechanism for the hump that Fulton did not measure and we cannot cite. What it establishes is narrow and worth saying plainly: steareth-10 is the single highest-scoring member of its own series, and its number is not explained by the ethoxylation rule that explains its cousins.
What the evidence doesn’t tell you
Everything above happened inside the ear of a rabbit: the ingredient at roughly 10% in propylene glycol, 1 ml applied to the inner ear of three New Zealand albino rabbits, five days a week for two weeks, follicles then scored for keratosis. It is not a human face and not a finished formula. That roughly 10% is the assay concentration; we hold no measured in-use figure for steareth-10 to set beside it. We identified no human comedogenicity study of steareth-10 — not on a face, not on a back, not with a comedone count anywhere. And it was read once. Fulton scored steareth-10 in his 1989 survey and, as far as the record we hold goes, nowhere else. We hold his earlier 1984 rabbit-ear table in full, and it has no steareth row at all; the steareth series appears only in 1989. So there is no second Fulton reading of this material to compare against. Morris and Kwan, whose 1983 assay ran on the same 0-to-5 scale and who were willing to contradict Fulton in print, tested five surfactants and steareth-10 was not among them. We identified no non-Fulton measurement of steareth-10's comedogenicity. The 4 is a single reading by a single investigator on a single model, and that is the whole of the numeric record in the inventories we searched — which is worth keeping in mind next to the confident-looking place it holds at the top of its own family: the peak is real in Fulton's table, and Fulton's table is the only place we have found it read. The "10" is itself an average, not a specification. Steareth-10 is not a pure compound but a distribution of stearyl alcohol carrying a spread of ethylene-oxide chain lengths that average about ten. Fulton reports no supplier, no certificate of analysis and no measured distribution for the material behind his row, so what exact mixture scored the 4 is not recoverable — a caveat that sits under every ethoxylate score, and one his non-monotonic column makes concrete rather than theoretical. Fulton rejected the low-concentration defence in general — his conclusion says "we are not convinced of the statement that lower concentrations of these compounds can be safely used with no comedogenic consequences" — but that sentence names isopropyl myristate, acetylated lanolin alcohol and lauric acid derivatives such as laureth-4, and it does not name steareth-10. He published no dose-response curve for it, and we identified no study establishing a percentage below which it stops producing comedones in the assay. Finally, the field-wide caveat that sits under every legacy score on this site: a 2025 review in JAAD Reviews, surveying the literature from 1972 on, found that no standardised comedogenicity test exists and that "non-comedogenic" is an unregulated label. That is a remark about the standards of this subject, and it applies to steareth-10's 4 exactly as it applies to everyone else's numbers.
Where you’ll see it
On a label it is Steareth-10. The CIR's 2012 report on the alkyl PEG ethers records the steareths across skin, hair and bath products; in practice a mid-ethoxylated steareth like this one is an oil-in-water emulsifier, so it shows up most visibly in creams, lotions and emulsion cleansers, where its job is to keep an oil phase and a water phase from separating. Those are illustrative categories, not a measured prevalence — we have not audited the market — and we are not going to tell you where it sits on an ingredient list, because label position is not a dose. Its ethoxylate relatives are separate entries here with their own scores, and — per Fulton's own table — not the same score. Reading across the steareths, steareth-10 is the one that scored highest; the more heavily ethoxylated steareth-20 and steareth-100 read lower, and so does the barely ethoxylated steareth-2. If you are scanning a label for the members Fulton scored positive, it is this one, at ten, and not the family in general.
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 of our legacy score and of nearly every comedogenic number in circulation. Method: the ingredient at roughly 10% in propylene glycol, 1 ml applied to the inner ear of New Zealand albino rabbits, three rabbits per assay, five days a week for two weeks, follicles scored for keratosis on a 0–5 scale. Read off a transcription of Table I, not off a chart quoting it. It prints Steareth-10 at 4 — a row for the declared material itself, though commercial Steareth-10 is a distribution of chain lengths around an average of ten ethylene-oxide units and Fulton reported no supplier, distribution or purity — alongside the rest of its series: Steareth-2 at 2, Steareth-20 at 2 and Steareth-100 at 0, so the score peaks at steareth-10 rather than falling monotonically with ethoxylation the way the oleth rows (5, 3, 2, 1) and the laureth pair (5, 3) do. It supplies the grade key the charts omit ("0 to 1 not significant, 2 to 3 borderline, 4 to 5 positive"). Its conclusion names "the major offenders" — isopropyl myristate, acetylated lanolin alcohol and lauric acid derivatives such as laureth-4 — and does NOT name steareth-10. A rabbit-ear assay, and the author himself called the survey "not at all definitive but simply designed to stimulate research."
- Fulton JE, Pay SR, Fulton JE III. "Comedogenicity of current therapeutic products, cosmetics, and ingredients in the rabbit ear." J Am Acad Dermatol 10(1):96–105 (1984) Fulton's earlier rabbit-ear paper, on the same 0–5 scale. Cited here for what it does NOT contain: its ingredient table has no steareth row of any length — the steareth series appears only in the 1989 survey — which is why this page can say steareth-10's 4 was read only once. We hold its Table I in full (print copy read at 400dpi); the absence is verified, not assumed. Its surfactant section runs myristyl lactate, isopropyl myristate, myristyl myristate, butyl stearate, isopropyl isostearate, isostearyl neopentanoate, isopropyl palmitate, decyl oleate, PPG-2 myristyl propionate, laureth-4 and sodium lauryl sulfate, and stops there.
- Morris WE, Kwan SC. "Use of the rabbit ear model in evaluating the comedogenic potential of cosmetic ingredients." J Soc Cosmet Chem 34:215–225 (1983) An independent primary assay on the same 0–5 scale, six years before Fulton 1989 — not a republisher of him, and willing to contradict him in print. Cited here for what it does NOT contain: the five surfactants it tested were two sodium lauryl sulfate dilutions, ammonium lauryl sulfate, octoxynol-9 and polysorbate 20, and no steareth appears among them. It is the reason this page can say there is no non-Fulton measurement of steareth-10 to check the 4 against. We hold its transcribed rows in full; the absence is verified, not assumed.
- Fiume MM, Heldreth B, Bergfeld WF, et al. (Cosmetic Ingredient Review Expert Panel). "Safety Assessment of Alkyl PEG Ethers as Used in Cosmetics." Int J Toxicol 31(5 Suppl):169S–244S (2012) An independent expert-panel safety review of a large family of alkyl PEG ethers, the steareths among them, and NOT a comedogenicity assessment. Cited only for what it actually establishes: that the steareths function as surfactants and emulsifiers, and that the Panel concluded the alkyl PEG ethers safe as used when formulated to be non-irritating. It assesses safety, not pore-plugging — a different question — and says nothing about comedones. It also notes that these ethoxylates can carry 1,4-dioxane as a manufacturing impurity, which is a purity-and-safety matter, not a comedogenicity one, and not to be borrowed as if it were.
- "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 the literature from 1972 onward, and independent of Fulton and of the charts that republish him. Finds that no standardised comedogenicity test exists and that "non-comedogenic" is an unregulated label. Cited for the field-wide caveat that sits under every legacy score on this site, steareth-10's included.
Others in the same family
Ethoxylates (PEGs & polysorbates) behave similarly enough that the evidence for one is often wrongly read across to the others. These are its structural relatives, not a guess. What the evidence says about ethoxylates (pegs & polysorbates) as a family ›
Last reviewed 2026-08-12 · How we decide