Laureth-23
Laureth-23 is the heavily ethoxylated end of the laureth series, and the comedogenic number it carries is a real one: Fulton's 1989 rabbit-ear assay scored it 3 on his 0-to-5 scale, in a row printed under this ingredient's own name. But a 3 sits at the top of the band Fulton himself called borderline, it is lower than the 5 he gave laureth-4, and it is a single reading — one investigator, one model, three rabbits' ears, with no human test and no second laboratory behind it.
Fulton 1989 rabbit ear 3 of 5 - borderline by his own key, not positive. One reading, no human data.
What it is
Laureth-23 is a nonionic surfactant made by attaching a long chain of, on average, twenty-three ethylene-oxide units to lauryl alcohol — the twelve-carbon fatty alcohol that corresponds to lauric acid. On a label it is Laureth-23, and the "23" is that average number of ethylene-oxide units; like all ethoxylates it is a distribution around that mean rather than a single molecule. Its CAS number is listed as 9002-92-0 — a registry number that covers the polyoxyethylene lauryl ethers generally rather than one that fixes the average at twenty-three ethylene-oxide units — and it is also sold under the trade names Brij 35 and Brij L23. The Cosmetic Ingredient Review's 2012 assessment of the alkyl PEG ethers describes the laureths as reaction products of lauryl alcohol and ethylene oxide, and lists the family's cosmetic functions as surfactant and emulsifier. The long ethylene-oxide chain makes laureth-23 strongly water-loving — a high-HLB emulsifier, the kind a formulator reaches for to hold an oil-in-water emulsion together or to dissolve a small amount of oil or fragrance into a watery base. That is the opposite end of the series from laureth-4, whose short four-unit chain leaves it oil-loving and suited to oil cleansers; the two share a backbone but do different jobs in a formula, and they do not carry the same rating here.
Why we rate it Caution
We rate it Caution, at Low confidence, and the number behind that rating is genuine. Fulton's 1989 table — the source of nearly every comedogenic number in circulation — prints Laureth-23 at 3 on his 0-to-5 scale. We read the row off a transcription of Table I rather than off a chart quoting it: the row is Laureth-23, a match at the level of the ingredient name, not a neighbouring ethoxylate and not the parent alcohol. It carries no asterisk, no range and no parenthesis, and it is not one of the rows in the oils section, whose heading carries Fulton's "results depend on source of raw material" footnote. So it is a single unstarred reading of 3 on a 0-to-5 scale, which is not the same as a demonstration that every commercial grade of laureth-23 would read the same. Fulton names no supplier, and the absence of his oils footnote is the absence of a notation, not evidence of grade-invariance. What a 3 means is the whole of this page, because the charts that republish Fulton's numbers leave his key out. In his own words: "0 to 1 is not considered significant, 2 to 3 is borderline, 4 to 5 is considered positive." A 3 is the top of the borderline band — not the positive territory of a 4 or 5, and not the clean nothing of a 0 or 1. Caution is the rating that matches a borderline result: neither a warning nor an all-clear. Two things Fulton did for laureth-4, he did not do for laureth-23, and the difference is worth stating plainly because it is the difference between the two ratings. He named laureth-4 in his conclusion — "the major offenders, such as isopropyl myristate, acetylated lanolin alcohol, and lauric acid derivatives such as laureth-4" — and he read it twice. The 1984 paper prints Laureth-4 at 4 of 5, carrying that paper's concentration asterisk (diluted in mineral oil, or made up as a 10% alcohol gel, rather than applied as is), and 1984 runs a different threshold from 1989: there, "a grading score of 3 or above is considered positive." So laureth-4 read positive in 1984 by the 1984 key and positive again in 1989 by the 1989 key. Laureth-23 appears in neither the offenders sentence nor the 1984 table. It has one reading, from one year, and Fulton singled out its sibling, not it. There is a pattern in the table that this page can point to but must not oversell. Within the laureth pair, the lightly ethoxylated laureth-4 scored 5 and the heavily ethoxylated laureth-23 scored 3; Fulton's oleth rows run the same direction (Oleth-3 a 5, Oleth-5 a 3, Oleth-10 a 2, Oleth-20 a 1). More ethylene-oxide units, lower score, across those rows. That is a set of numbers printed in one table, not a law and not a mechanism — Fulton's own note on the lanolins runs the other way, saying the classic anhydrous lanolins "are not as comedogenic as the moderately ethoxylated derivatives (laneth 10)" — so we report it as rows and leave the causation unclaimed. Nothing on this page should be read as saying that adding ethylene-oxide units is what lowered the score.
What the evidence doesn’t tell you
The 3 happened inside the ear of a rabbit: roughly 10% in propylene glycol, applied to the inner ear of New Zealand albino rabbits, follicles scored for keratosis. It is one reading. We identified no human comedogenicity study of laureth-23 — no comedone count, no follicular biopsy, on a face or a back — and we identified no second laboratory that tested it. 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, two of them nonionic ethoxylates (octoxynol-9 and polysorbate 20), but not this one; Fulton's own earlier 1984 table has no laureth-23 row. So unlike laureth-4, which Fulton read twice, laureth-23's number rests on a single measurement by a single investigator, and nothing we can find confirms or challenges it. "Borderline" is not "clear," and the honest reading of a 3 has to hold both halves. It is not the significant-positive result the top of the scale would be, and this page should not let the correction — that laureth-23 scored lower than laureth-4 — slide into a suggestion that it is inert. Fulton put a 3 at the upper edge of his borderline band for a reason, and we identified no evidence that walks it back. The "23" is an average. Commercial laureth-23 is a distribution of chain lengths around twenty-three ethylene-oxide units, not a pure compound, and a rabbit-ear score for one supplier's material is a score for one such distribution. The Cosmetic Ingredient Review's 2012 report on the alkyl PEG ethers concluded the family safe as used when formulated to be non-irritating, and noted that these ethoxylates can carry 1,4-dioxane and unreacted ethylene oxide as manufacturing impurities. That is a safety-and-purity assessment, not a comedogenicity one — it does not measure pores, and safety and comedogenicity are different questions. Finally, the caveat that sits under every legacy score on this site: the rabbit-ear model has been questioned since Frank's 1982 paper, and a 2025 review in JAAD Reviews, surveying the literature from 1972 onward, found that no standardised comedogenicity test exists and that "non-comedogenic" is an unregulated label. Laureth-23's rating is as well-supported as a single rabbit-ear reading can make it, which is to say: supported, and thin.
Where you’ll see it
On a label it is Laureth-23. The Cosmetic Ingredient Review's 2012 report on the alkyl PEG ethers records the laureth family across bath, cleansing, hair and sunscreen products, and that use table is the only sourced statement we have about where the family appears. Its listed function — emulsifier and solubiliser — is the job it does in a formula, holding oil in water or carrying a small amount of oil or fragrance in a watery base; that is a formulation role, not a claim about how often it appears or what it does to a pore. Its ethoxylate relatives are separate entries here with their own scores, and — per Fulton's own table — not the same score: the lightly ethoxylated laureth-4 reads higher, at the top of his scale.
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, applied to the inner ear of New Zealand albino rabbits, three rabbits per assay, follicles scored for keratosis on a 0–5 scale. Read off a transcription of Table I, not off a chart quoting it. It prints Laureth-23 at 3 — a row under this ingredient's own name, with no asterisk, range or parenthesis — alongside Laureth-4 at 5 and the oleth series (Oleth-3 5, Oleth-5 3, Oleth-10 2, Oleth-20 1). It supplies the grade key the charts omit ("0 to 1 not significant, 2 to 3 borderline, 4 to 5 positive"), and its conclusion names "lauric acid derivatives such as laureth-4" — not laureth-23 — among "the major offenders." A single rabbit-ear reading; Fulton himself called the survey "not at all definitive."
- 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 — two New Zealand albino rabbits per test, one ear dosed daily for two weeks and the other ear the control — on the same 0–5 scale but with a different threshold ("1 to 2 is not significant; a grading score of 3 or above is considered positive"). Cited here for two things it does not contain and one it does. Its Table I has NO Laureth-23 row, so it supplies no second reading of this material; it does print Laureth-4 at 4, carrying the paper's concentration asterisk (diluted in mineral oil or made up as a 10% alcohol gel). Because its key differs from the 1989 key, a number from this paper cannot be compared with a 1989 number without carrying both keys.
- 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) The other 0–5 rabbit-ear assay, from a different laboratory, and the one paper of the era willing to contradict Fulton in print. Thirty-two rows, of which five are surfactants — including two nonionic ethoxylates, octoxynol-9 and polysorbate 20 — and none is laureth-23. Cited only as the second lab that could have confirmed or contradicted Fulton's 3 and did not test the material, not as evidence about laureth-23 either way.
- 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 the alkyl PEG ethers, the laureth family among them, and not a comedogenic assessment. Cited only for what it actually establishes: that the laureths are reaction products of lauryl alcohol and ethylene oxide, that they function as surfactants and emulsifiers, and that the Panel concluded the alkyl PEG ethers safe as used when formulated to be non-irritating. It notes these ethoxylates can carry 1,4-dioxane and unreacted ethylene oxide as manufacturing impurities — a purity-and-safety matter, not a comedogenicity one. It assesses safety, not pores, and says nothing about follicular plugging.
- Laureth-23 INCI entry, SpecialChem Cosmetics Ingredients directory A cosmetic-ingredient reference listing, cited only for identity, not for comedogenicity: it records Laureth-23's CAS number (9002-92-0), its trade names (Brij 35, Brij L23), its derivation from lauryl alcohol and roughly 23 ethylene-oxide units, and its function as a nonionic surfactant, emulsifier and solubiliser. A supplier-facing INCI database, not a study and not evidence of any effect on skin.
- "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, laureth-23'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 2026-08-01 · How we decide