PEG-100 Stearate
PEG-100 stearate is one of the ethoxylate emulsifiers whose circulating comedogenic number is a genuine measurement of the exact material: Fulton's 1989 rabbit-ear assay scored it 0, the bottom of his scale. It sits in a family whose lightly ethoxylated members scored 4 and 5, and the same table shows the score falling as the stearate is ethoxylated further — PEG-8 stearate 3, PEG-20 stearate 1, PEG-100 stearate 0. It is still one reading, by one investigator, in three rabbits' ears, with no human test and no repeat reading in the inventories we searched.
Very common PEG emulsifier (usually paired with glyceryl stearate); rated non-comedogenic.
What it is
PEG-100 stearate is a nonionic surfactant made by esterifying stearic acid — the eighteen-carbon saturated fatty acid — with a polyethylene-glycol chain of, on average, 100 ethylene-oxide units. On a label it is PEG-100 Stearate, and the "100" is a nominal average rather than a count — a commercial grade is a distribution of chain-length homologues, and of monoester and diester, around that average, and Fulton characterises no supplier or grade for the material he scored. It is an oil-in-water emulsifier: the long, water-loving PEG chain and the fatty stearate tail let it hold an oil phase dispersed in water, which is why formulators reach for it in lotions and creams. In practice it is most often sold and used as a blend with glyceryl stearate — the trade materials Arlacel 165, Emulgade 165 and their equivalents — so on an ingredient list "Glyceryl Stearate (and) PEG-100 Stearate" is the pairing you will usually meet; we hold no supplier specification for the ratio in which the two are combined. Two neighbours are worth keeping apart from it, because the legacy table scores them differently. PEG-100 distearate — the same PEG-100 chain carrying two stearate groups rather than one — is a separate row, and Fulton scored it 2, not 0. Steareth-100 is a different molecule again: an ether of stearyl alcohol rather than an ester of stearic acid, though Fulton also scored it 0. Only PEG-100 stearate itself is the material this page is about.
Why we rate it Clear
We rate it Clear, at Low confidence. The number behind that rating is a single rabbit-ear reading, and the Low is because that reading is the whole of the evidence. Fulton's 1989 table — the source of nearly every comedogenic number in circulation — prints PEG 100 stearate at 0 on his 0-to-5 scale. We read the row off a transcription of Table I rather than off a chart quoting it, and it is unambiguous: the row is PEG 100 stearate, the monoester, not PEG 100 distearate (which he scores 2) and not Steareth-100 (a different molecule, which he also scores 0). It matters what a 0 is in Fulton's own words, because the charts that publish his numbers drop his key: "a minimal grade of 0 to 1 is not considered significant." A 0 is the clean bottom of that band — not "borderline," which is where his 2 and 3 sit. The reason to write this page at all is the company the 0 keeps. This family is where most of Fulton's 4s and 5s live: laureth-4 scored 5, oleth-3 scored 5, PPG 5 ceteth 10 phosphate scored 4. And his own stearate rows run in order — PEG 8 stearate 3, PEG 20 stearate 1, PEG 100 stearate 0 — the same acyl group carrying more ethylene-oxide units at each step, and the score falling at each step. His laureth and oleth rows fall the same way. That is the strongest single-family version of the pattern he recorded, because it holds the fatty part constant and varies only the chain length. It is a set of rows, not a law and not a mechanism, and the honest way to read it is with its exceptions in view: his steareth rows do not fall cleanly in order (Steareth-2 a 2, Steareth-10 a 4, Steareth-20 a 2, Steareth-100 a 0), and PEG 100 distearate — the same chain length but a second stearate group — scored 2 rather than 0. So heavy ethoxylation travels with a low score here, and we report it as that: the rows, and the places they break.
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, and how that roughly 10% assay concentration relates to the levels the ingredient is actually used at is unestablished — we hold no use-concentration figure for it. We identified no human comedogenicity study of PEG-100 stearate — not on a face, not on a back, not with a comedone count anywhere. And it was read once. PEG-100 stearate appears in Fulton's 1989 survey and nowhere else in the numeric record we hold: his earlier 1984 rabbit-ear table has no PEG-stearate row at all, and Morris and Kwan — whose 1983 assay ran on the same 0-to-5 scale, and who were willing to contradict Fulton in print — did not test it. We identified no non-Fulton measurement of PEG-100 stearate's comedogenicity. The 0 is a single reading by a single investigator on a single model, and it is the whole of the numeric record across the four inventories we searched — Fulton 1989, Fulton 1984, Morris and Kwan 1983, and Nguyen 2007. That cuts a particular way for a low score, and it is worth being exact about the direction: a rabbit ear Fulton himself called so sensitive that "not everything that irritates this model will also irritate human skin" returning a clean 0 is more reassuring than a positive from it would be alarming — but "one sensitive assay found nothing" is a narrower statement than "it is non-comedogenic," and only the first is what we hold. The safety record for PEG-100 stearate is far larger than its comedogenicity record, and the two are not the same question. The Cosmetic Ingredient Review has assessed the PEG stearates as a group since 1983 and judged them safe as used, on irritation, sensitization and long-term feeding data. None of that is a comedogenicity measurement. Safety is not the same endpoint as follicular plugging: a panel concluding an ingredient is non-irritating and non-sensitizing has said nothing about whether it clogs a pore. The same reviews note that PEG ethoxylates can carry trace 1,4-dioxane and ethylene oxide as manufacturing impurities — a purity-and-safety matter, and again not a comedogenicity one. Almost all of PEG-100 stearate's real-world use is inside a blend with glyceryl stearate, and Fulton tested the single ingredient, not the blend. A score for PEG-100 stearate on its own is not a score for "Glyceryl Stearate (and) PEG-100 Stearate," and neither is a score for a finished cream built on that emulsifier. Fulton's own conclusion rejected the general assumption that lower in-use concentrations are automatically safe — "we are not convinced of the statement that lower concentrations of these compounds can be safely used with no comedogenic consequences" — though that sentence was aimed at his positive scorers, not his zeros. 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 applies to PEG-100 stearate's 0 as it applies to everyone else's numbers.
Where you’ll see it
On a label it is PEG-100 Stearate, and it most often appears immediately after Glyceryl Stearate, as the pair "Glyceryl Stearate (and) PEG-100 Stearate" — the two are sold together as a single nonionic oil-in-water emulsifier system (Arlacel 165, Emulgade 165, Lexemul 561 and equivalents). The Cosmetic Ingredient Review records the PEG stearates in use across cosmetic product categories as surfactants and emulsifying agents; in practice this pairing is a workhorse emulsifier in moisturisers, lotions, creams, cleansers and sunscreens. Those are illustrative categories, not a measured prevalence — we have not audited the market — and label position will not tell you a concentration. Its ethoxylate relatives are separate entries here, and per Fulton's own table not the same score: the lightly ethoxylated members of the stearate, laureth and oleth series read much higher than the heavily ethoxylated ones. PEG-100 distearate and Steareth-100 are different materials again.
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 PEG 100 stearate at 0 — an exact row for this exact material — alongside its ethoxylation series (PEG 8 stearate 3, PEG 20 stearate 1) and distinct from PEG 100 distearate (2) and Steareth-100 (0). The same table carries the family's high scores (Laureth-4 5, Oleth-3 5) and supplies the grade key the charts omit ("0 to 1 not significant, 2 to 3 borderline, 4 to 5 positive"). 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: it has no PEG-stearate row at all — the PEG stearate series appears only in the 1989 survey — which is why this page can say the 0 was read only once. We hold its Table I in full, so the absence is verified, not assumed. It is not an independent laboratory, and it is still a rabbit's ear.
- Elder RL (ed.), Cosmetic Ingredient Review. "Final Report on the Safety Assessment of PEG-2, -6, -8, -12, -20, -32, -40, -50, -100, and -150 Stearates." J Am Coll Toxicol 2(7):17–34 (1983); reaffirmed 2002; re-reviewed by Fiume MM et al. (2025) An independent expert-panel SAFETY review of the ten PEG stearates, PEG-100 stearate among them, and NOT a comedogenicity assessment. Cited only for what it actually establishes: that the PEG stearates function as surfactants and emulsifying agents and are used across cosmetic product categories, and that the Panel judged them safe as used — nonlethal at up to 10 g/kg, minimally irritating at 100%, and neither irritants nor sensitizers in clinical testing at 25% or greater. It assesses safety, not pore-plugging — a different endpoint — and says nothing about comedones. It also notes these ethoxylates can carry trace 1,4-dioxane and ethylene oxide as manufacturing impurities, which is a purity-and-safety matter and not a comedogenicity one.
- "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, PEG-100 stearate's 0 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