Porecelain

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Isopropyl Isostearate

Isopropyl isostearate is rated Clogging, and the number behind it is better corroborated than most on this site: four exact-name rabbit-ear results from three research groups, none of them low. Fulton printed 5 of 5 twice, Morris and Kwan 4 of 5 six years before him, and a 2007 assay on a different scale called it positive. All four read rabbit ears, not human faces.

Clogging Low confidence Legacy score 5 on a 0-5 scale · Fulton 1989 · low reliability

Fulton 1989 and 1984 both printed 5 of 5; Morris and Kwan 4 of 5. Rabbit-ear only, no human data found.

What it is

Isopropyl isostearate is the isopropyl ester of isostearic acid — a branched eighteen-carbon fatty acid. It is a lightweight emollient ester: a formulator uses it for slip and spreadability, for a dry, non-greasy skin feel, and as a solvent that wets pigments and dissolves other oil-phase ingredients. On a label it is Isopropyl Isostearate. It belongs to the isopropyl-ester family, the same short-alcohol esters as isopropyl myristate and isopropyl palmitate, and that family connection matters on this page — but keep the members separate, because one of them is the very thing the comedogenic scale is calibrated against, and this is not it. A note on the name only, not a mechanism: isostearic acid is methyl-branched, which is what distinguishes it from straight-chain stearic acid. We mention that because it is what the "iso" means, not because we can tell you the branch is responsible for anything the assays measured. It is also not isopropyl stearate, which is the ester of the straight-chain acid and has its own record.

Why we rate it Clogging

We rate it Clogging at Low confidence, and the confidence is Low for one plain reason: every number behind this rating comes from a rabbit's ear. What is unusual — and worth the page — is that the number itself is one of the better-corroborated ones on this site. Four papers printed a result for this exact ingredient name, three research groups produced them, and we have found none that reads low. What the primary table prints. Fulton's 1989 rabbit-ear survey, the source of nearly every comedogenic score in circulation, lists "Isopropyl isostearate — 5" in Table I, on his 0–5 scale. The cell carries no asterisk and no range — it is a flat 5 — and the row sits well outside the asterisked Oils section, so it does not inherit the "results depend on source of raw material" caveat that hangs over every oil and butter he scored. By Fulton's own published key — the part almost nobody quotes — "a grade of 4 to 5 is uniformally reproduceable and considered positive," while a 2 to 3 is only "borderline." So a 5 sits at the top of the scale, in the band Fulton called positive, not in the borderline middle. The one distinction that has to be made here, because it is exactly the trap this site exists to catch. Isopropyl isostearate's near-namesake, isopropyl MYRISTATE, also scores 5 in that table — but that 5 is not a measurement. Fulton defined the top of his 1989 scale by it: grade 5 is "the presence of large comedones throughout the ear, similar to those induced by the application of our standard 'positive' testing agent, isopropyl myristate." Isopropyl myristate is the ruler. Isopropyl isostearate is a different molecule that was laid against that ruler and read at the top of it. Its 5 is a reading; its cousin's 5 is the mark the reading is taken from. They are one letter apart on a label and they are not the same kind of fact. Now the part that is rare here. Most scores on this site trace to a single assay quoted many times. This one does not. Morris and Kwan, publishing in the same journal six years BEFORE Fulton's survey and in a different laboratory, scored "Isopropyl Isostearate" 4 on the same 0–5 scale, applied undiluted. Morris and Kwan are not a Fulton republisher — they tested independently, and they contradict him in print on other materials: of sodium lauryl sulfate they wrote that their own finding of noncomedogenic activity "conflicts with the high scores published by Fulton et al.," and they read isocetyl stearate at 0–1 of 5 where Fulton's 1984 abstract had named it an offender without giving it a number. On this ingredient they agree with him — both put it near the top of the same scale. We hold their number and not their grading key, so we will not tell you which band Morris and Kwan themselves called positive; what we can say is that a 4 sits near the top of the scale they used. Fulton's earlier 1984 rabbit paper, which we have read in full, prints "Isopropyl isostearate — 5" a third time and names the ingredient outright in its abstract, among "isopropyl myristate and its analogs," as an offender. That paper is a second reading, not a second laboratory: James Fulton led both. It also runs a different key and a different anchor — in 1984 a 3 or above is "considered positive," and grade 5 is defined by comedones "similar to those induced by the application of coal tar," not by isopropyl myristate. Two rulers, five years apart, and the same ingredient name read at the top of each. The fourth reading is the newest and the one this page previously missed. Nguyen, Dang and Maibach tested fourteen cosmetic materials in the rabbit ear in 2007 and reported that the first nine, of which isopropyl isostearate is the fourth listed, "were deemed positive." That assay runs a 0–4 scale of its own, so its result cannot be added to or averaged with the 0–5 numbers, and we carry no number from it at all: we have read its published abstract and not its full text. What it establishes is direction, from a group with no connection to Fulton, eighteen years after his survey. So: four exact-name results, three research groups, two of them outside the Fulton lineage. Fulton's two 5s each sit in the band his own paper called positive; Nguyen and colleagues used the word positive themselves; Morris and Kwan printed a 4 of 5 without a key we have read, and nothing in the record reads this ester as inert. That is a good deal more agreement than most of the numbers this site examines can show, and it is why the Clogging rating is not one we have any quarrel with. It is still four rabbit ears.

What the evidence doesn’t tell you

It is still all rabbit ear, and the confidence tier says so. We identified no human comedogenicity study of isopropyl isostearate specifically — no facial trial, no follicular-biopsy study of this ester on a person. Everything above is a variant of one animal model, and the variants are not identical: Fulton 1989 applied roughly 10% in propylene glycol to the inner ears of three New Zealand albino rabbits, five days a week for two weeks; Fulton 1984 used two rabbits, one ear dosed daily for two weeks with the other ear as its control, and — the row being unstarred, and the paper's footnote reserving dilution for starred rows — apparently applied the material as it came; Morris and Kwan applied it undiluted, fourteen doses, grading follicles under a microscope; Nguyen and colleagues used a 0–4 scale we cannot convert into the others. Four readings of one ingredient name is not four measurements of one thing. None of the papers records a supplier, a purity, or which branched C18 isomers were in the bottle, and "isostearic acid" is a commercial description rather than a single compound. Concentration is the caveat that cuts hardest. The recorded conditions are undiluted, apparently as-is, and roughly 10%; isopropyl isostearate appears in real products at far lower levels, and a reading taken at 10% to 100% says very little about what a fraction of a percent does in a lotion. There is a dose-response series in circulation for this ester — a 4 at 100% falling to 2–3 at 50% and 1–2 at 5%, all on a 0–5 scale — and it is the kind of tidy sequence that completes an argument, which is why we went looking for where it comes from. It is not untraceable: Michelle Wong's Lab Muffin fact-check of comedogenicity ratings prints that series, and comparable series for other esters, and cites Draelos and DiNardo 2006 for them — the same paper cited below. We have not read that paper's full text, so we do not carry its numbers; and note that the 4 at 100% is not a garbled version of Fulton's 5, it is the same figure Morris and Kwan printed for undiluted material, though we have not traced whether one is the source of the other. What we can say from documents we have read is narrow: the four assays used undiluted or roughly 10% material, and none of them measured a low concentration of this ester. Fulton, for his part, wrote in his 1989 conclusion that he was "not convinced of the statement that lower concentrations of these compounds can be safely used with no comedogenic consequences." Read that sentence in place: "these compounds" are the offenders he had just named — isopropyl myristate, acetylated lanolin alcohol and lauric acid derivatives such as laureth-4 — and isopropyl isostearate is not among them. It is an opinion he stated about a set this ester was not listed in, not a low-dose result he reported for it. The rabbit-ear method itself has been contested for decades. Frank, in the Journal of the American Academy of Dermatology in 1982, asked whether the model in its then-present state was prophetic of acnegenicity at all, citing the problems of performing the test and the absence of correlation with human experience. Draelos and DiNardo, in a 2006 "Current Issues and Opinion" piece, tested finished products on human upper backs and found some testing non-comedogenic despite containing ingredients the rabbit assay had scored as offenders — a finding about formulas, not a head-to-head validation of the model, but a real caution against reading an ingredient score as a verdict on the product it ends up in. A 2025 JAAD Reviews survey of the field concluded that no standardised comedogenicity test exists and that "non-comedogenic" is an unregulated label. Those objections apply to this 5 as much as to any score. The difference, on this page, is only that when separate groups tested materials sold under the same name they landed in the same place — which raises the odds the reading is real without doing anything to close the gap between a rabbit's ear and a face. And none of it says what a finished product does: the four assays measured an ingredient, not a formula, and Draelos and DiNardo's human panels are the reason we will not read an ingredient score as a verdict on the lipstick it ends up in. One thing we set aside deliberately. The Elelaf comedogenic ingredient checker lists isopropyl isostearate among five "high confidence comedogenic" ingredients and adds "Documented in human models." We identified no human model for this ingredient, and we are not going to borrow a confidence we cannot source.

Where you’ll see it

On a label it reads Isopropyl Isostearate. It turns up as a lightweight emollient and pigment-wetting agent in colour cosmetics — lipsticks, foundations, cream blushers — and in cleansing oils and balms, some moisturisers, and hair products, where its dry slip is wanted. Those are illustrative categories, not a measured prevalence: we have not audited the market, and where it sits on an ingredient list is not a measure of how much is in the jar.

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.

  1. 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 origin of essentially every comedogenic number in circulation. Read off a 400dpi render of the table transcribed in this repository, not via a list quoting it. Table I prints "Isopropyl isostearate — 5" — no asterisk, no range — in the ester rows, outside the asterisked Oils section. Method: ingredient at roughly 10% in propylene glycol, applied to the inner ear of three New Zealand albino rabbits, five days a week for two weeks, follicular keratosis measured under a micrometer. Fulton's grading key: 0–1 "is not considered significant," 2–3 is "borderline," 4–5 is "considered positive." Note that grade 5 is DEFINED by a different molecule — Fulton set the top of his scale as comedones "similar to those induced by our standard positive testing agent, isopropyl myristate" — so isopropyl isostearate's 5 is a measurement against that standard, not the standard itself. Fulton called the survey "not at all definitive but simply designed to stimulate research."
  2. 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 rabbit-ear assay on the same 0–5 scale, six years BEFORE Fulton 1989 and from a different laboratory — not a republisher of him. It scores "Isopropyl Isostearate" 4. This is the corroboration that makes the page: Morris and Kwan tested independently and contradict Fulton in print on other materials — they write that their finding of noncomedogenic sodium lauryl sulfate "conflicts with the high scores published by Fulton et al.," and they read isocetyl stearate at 0–1 — so their agreement here is not an echo. Method: rabbit ear canal, three rabbits, applied undiluted unless otherwise stated, fourteen applications, microscopic follicular grading. Thirty-two rows only, and its oils table is printed rotated on the page so OCR returns nothing for it, which is why sites that scraped this paper by machine lost half of it.
  3. Fulton JE, Pay SR, Fulton JE III. "Comedogenicity of current therapeutic products, cosmetics, and ingredients in the rabbit ear." J Am Acad Dermatol 10:96–105 (1984) Fulton's earlier rabbit-ear paper, by the same lead author, read in full (print copy obtained 18 July 2026) and transcribed in this repository. Its Table I prints "Isopropyl isostearate — 5" on the 0–5 scale, unstarred, and its abstract names the ingredient explicitly, among "isopropyl myristate and its analogs," as an offender. Method: two New Zealand albino rabbits per test, one ear dosed daily for two weeks against the other ear as control; per the paper's footnote, liquids and soft solids were used "as is" and only starred rows were diluted. Its threshold key differs from 1989's — in 1984 a 3 or above is "considered positive," where in 1989 that band is 4–5 — and so does its anchor for grade 5, which is coal tar rather than isopropyl myristate. A 5 is positive under either key. Not an independent lab from the 1989 paper; a same-author corroboration.
  4. Nguyen SH, Dang TP, Maibach HI. "Comedogenicity in rabbit: some cosmetic ingredients/vehicles." Cutan Ocul Toxicol 26(4):287–292 (2007) A later rabbit external-ear-canal assay from a group unconnected to Fulton, on its own 0–4 scale — a different scale from the 0–5 papers, so its result cannot be merged with theirs. Read at the level of its published abstract only, via the US EPA's HERO bibliographic record (HERO ID 1616835), which reproduces the abstract in full because the publisher's page is behind a challenge screen. We did not obtain the full text, so we carry no number from it. The abstract lists fourteen tested materials in order — isopropyl palmitate, isopropyl myristate, butyl stearate, isopropyl isostearate, decyl oleate, isostearyl neopentanoate, isocetyl stearate, myristyl myristate, cocoa butter, cetyl alcohol, paraffin, stearyl alcohol, sodium lauryl sulfate and petrolatum — and states that "the first nine were deemed positive." Isopropyl isostearate is fourth. That is a positive classification of this exact ingredient name by a third group, and nothing more: no score, no concentration, no vehicle, no animal count for this material is recoverable from the abstract. Obtaining the table remains an open job.
  5. Draelos ZD, DiNardo JC. "A re-evaluation of the comedogenicity concept." J Am Acad Dermatol 54:507–512 (2006) The general critique of the rabbit-ear assay, cited here because it cuts against this 5 as much as against anyone's. A "Current Issues and Opinion" piece that tested FINISHED PRODUCTS on small human upper-back panels and found products testing non-comedogenic despite containing ingredients the rabbit assay had scored comedogenic. It is evidence that an ingredient's score does not transfer cleanly to the formula it ends up in — not a human re-test of this ester, which we did not find. It is also the paper Lab Muffin's fact-check of comedogenicity ratings cites for the circulating 100%/50%/5% dilution series for this ester; we have not read its full text and do not carry those numbers.
  6. Frank SB. "Is the rabbit ear model, in its present state, prophetic of acnegenicity?" J Am Acad Dermatol 6(3):373–377 (1982) The earliest peer-reviewed challenge to the assay every number on this page comes from. Cited for a caveat that applies symmetrically: the model's weaknesses undermine an alarming 5 exactly as much as a reassuring 0. It is a critique of the method, not a re-test of this ester.
  7. "Comedogenicity in cosmeceuticals - a review of clinical relevance, regulatory gaps, and future directions." JAAD Reviews (2025) A recent peer-reviewed narrative review of the whole field, covering literature from 1972 onward. A synthesis, not new data, and not independent of Fulton in the sense of testing anything. Cited only for the field-wide finding that no standardised comedogenicity test exists and that "non-comedogenic" is an unregulated label.
  8. Michelle Wong (Lab Muffin Beauty Science). "How to Use Comedogenicity Ratings" A cosmetic chemist's consumer-facing fact-check, not a primary assay. Cited for one narrow purpose only — it is where the circulating 100%/50%/5% dilution series for this ester appears with a citation attached (to Draelos and DiNardo 2006), which is how we traced a number we had seen floating unattributed. We have not read the paper it cites, so we treat the series as an attribution we have located rather than a result we hold.
  9. Elelaf Journal — "Comedogenic Ingredient Checker" A consumer ingredient checker, cited as the artefact under examination rather than as evidence. It lists isopropyl isostearate among five "high confidence comedogenic" ingredients and states "Documented in human models." It names no human study for this ester, and we identified none, so we do not adopt that confidence. Not a comedogenicity assay and it does not claim to be one.

Others in the same family

Esters 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 esters as a family ›

Last reviewed 2026-08-01 · How we decide

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