Porecelain

Flawless skin starts with the fine print.

Isopropyl Linoleate

Isopropyl linoleate is rated Clogging, and unlike several of the scores this site has had to take apart, its score is not the wrong molecule's and not a fabrication — it is a real reading, and a second laboratory read the same named ester high as well. Fulton printed it 4 on a 0-to-5 scale in 1989, under the older spelling "Isopropyl linolate", in the band he called positive; Morris and Kwan, in a different laboratory six years earlier, printed "Isopropyl Linoleate" at 4-5 on the same scale, near the top of it. Neither was a human face.

Clogging Low confidence Legacy score 4 on a 0-5 scale · Fulton 1989 · low reliability

Fulton 1989 prints Isopropyl linolate 4 of 5; Morris & Kwan 1983 print 4-5 of 5, another lab.

What it is

Isopropyl linoleate is the isopropyl ester of linoleic acid, the eighteen-carbon polyunsaturated omega-6 fatty acid. On a label it is Isopropyl Linoleate; its CAS number is 22882-95-7. A formulator reaches for it as an emollient and skin-conditioning agent — it softens and smooths the surface, gives a light slip, and is also used as a binding agent — which is how the Cosmetic Ingredient Review's record of the alkyl esters describes its function. One distinction is worth making at the top, because it is the whole reason this page has anything to add. Isopropyl linoleate is the isopropyl ester of linoleic acid. It is not free linoleic acid, and it is not linoleic acid bound as part of a natural triglyceride in a seed oil. Those are three different test materials, and the comedogenicity literature below tested only the ester. A reader who has heard that "linoleic acid is good for acne-prone skin" has heard something about a different material; that claim and this rating are not in contradiction, because they are not about the same substance.

Why we rate it Clogging

We rate it Clogging at Low confidence, because the evidence is the legacy rabbit-ear assay and nothing stronger. What this page adds is what kind of number the 4 is — and here, unusually, the answer is that it is a real reading, and that a second laboratory tested the same named ester and also read it high. Where the number comes from. James Fulton's 1989 survey in the Journal of the Society of Cosmetic Chemists is the source of nearly every comedogenic score in circulation, and we read its Table I off a render of the journal scan rather than a list quoting it. The row it prints for this material is spelled "Isopropyl linolate" — that is the paper's spelling, verbatim, and we have not tidied it — at a comedogenicity grade of 4 on a 0-to-5 scale, with no asterisk. The spelling is worth a sentence because on this site a name that is one letter off is usually the whole story: it is how a score ends up attached to a material that was never in the assay. Here it is not. "Linolate" is a variant form of "linoleate" and a documented synonym for the same ester, CAS 22882-95-7 — and, more to the point, Morris and Kwan print "Isopropyl Linoleate", in the modern spelling, and score it high too. That second row is what settles the identity question: the high reading does not depend on accepting Fulton's older spelling, because a paper using the current name found the same thing. The asterisk matters by its absence: Fulton attached it to his oils, where it means "results depend on source of raw material," and it does not attach to this ester, so the usual escape hatch for a high oil score is not available here. On Fulton's own published key, "a minimal grade of 0 to 1 is not considered significant," 2 to 3 is "borderline," and only "a grade of 4 to 5 is uniformally reproduceable and considered positive." The 4 sits in the one band he treated as a real finding rather than noise. A second reading, and it is genuinely independent. Morris and Kwan, in 1983 — six years before Fulton, in a different laboratory, on the same 0-to-5 scale — ran their own rabbit-ear assay and scored "Isopropyl Linoleate" 4-5, applied undiluted. This is not quite the same figure as Fulton's 4, and we are not going to round the two into a single number they do not jointly print. We also do not hold Morris and Kwan's own interpretive key, so we will not tell you which band they called positive; what we can say is that 4-5 sits at the top of the 0-to-5 scale they used. What the two labs agree on is direction: both read this ester high rather than in the noise. That is more than many numbers on this site have behind them: the two papers disagree on other materials, and Morris and Kwan say so in print. Here they do not. It is one of the higher ester results in the legacy record, but it is not the highest. Fulton's own 1989 table prints isopropyl isostearate and myristyl myristate at 5 — readings, not definitions — and his earlier 1984 paper prints several esters at 5 as well. A 4 is high; it is not the ceiling. The third legacy paper says nothing at all, which is worth stating rather than skipping. Fulton's earlier rabbit-ear paper with Pay and Fulton (1984) — read in full and transcribed in this repository — has no row for this ester under either spelling. It neither confirms nor contradicts the 1989 reading, and an absent row is not a zero. A word on the family's most famous number, because it is the thing to hold this one against. Isopropyl myristate carries a 5, the maximum — but that 5 is the scale's calibration point, not an independent result. Fulton defined the top of his scale by the response isopropyl myristate produces ("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"), so the sibling's 5 is circular by construction. Isopropyl linoleate's 4 is not: it is a neighbour graded against that scale, and it returned a high reading of its own — as did the same named ester in a second laboratory. So the rating is Clogging, and the honest account is this: two rabbit-ear assays, in two laboratories, scored isopropyl linoleate 4 and 4-5 on a 0-to-5 scale, high in both, and neither tested a human face, a finished formula, or a concentration anyone actually wears. The Low confidence is a statement about that gap, not about the agreement, which is real.

What the evidence doesn’t tell you

Everything above rests on rabbit ears. Fulton's method: the ingredient diluted to roughly 10% in propylene glycol, about 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 under a micrometer. Morris and Kwan ran a rabbit-ear assay too, on the ear canal, three rabbits, applying the material undiluted over fourteen applications and grading microscopically. Fulton said plainly that the rabbit ear is more sensitive than human skin, and warned that "not everything that irritates this model will also irritate human skin." Neither assay is a human face, a finished product, or an in-use dose. Neither paper tells you what it actually tested, beyond the name. No supplier, purity, grade or batch is recorded in either row, and we identified no record of the material either laboratory obtained. Two papers printing the same ingredient name is not a demonstration that they tested equivalent material, so read the agreement above as agreement between two printed names rather than proof that one substance was measured twice. Concentration is doing work the bare number hides. These assays test at high strength — Fulton at about 10%, Morris and Kwan undiluted — and we identified no comedogenicity result for this ester at any concentration below Fulton's roughly 10%. A comedogenic grade is a property of a material at a dose, not a fixed trait it carries into a 2% emollient. But Fulton distrusted exactly that reassurance: his conclusion reads, "We are not convinced of the statement that lower concentrations of these compounds can be safely used with no comedogenic consequences." He wrote that about the major offenders he had just named, and this ester is not one of them, so take it as his general position on dilution rather than a finding about isopropyl linoleate. It points both ways at once — against assuming a low percentage is automatically safe, while conceding that the safe threshold was never established for this material. We are not going to tell you why it clogs. The tempting move is to reach for a mechanism — that the ester spreads into the follicle, or that the polyunsaturated chain oxidises — and content mills state such things as fact. No comedogenicity paper we read demonstrates a mechanism for this molecule; the assays counted comedones, they did not explain them. A mechanism asserted to dress up a rating is not evidence. Human evidence: we identified no comedogenicity study that put isolated isopropyl linoleate on human skin and counted comedones. That absence is worth stating carefully, because there is a human study nearby that is easy to mistake for one and is not. Letawe, Boone and Piérard (1998), in a double-blind, placebo-controlled, randomised crossover, applied topical linoleic acid to patients with mild acne and measured microcomedones by digital image analysis of cyanoacrylate follicular biopsies; they reported roughly a 25% reduction in microcomedone size over a month, with no change at placebo sites, and concluded linoleic acid might act as a comedolytic. That is a real human result — but it tested free linoleic acid, not isopropyl linoleate. It is evidence about the free fatty acid, and this page is about its isopropyl ester. We note it precisely so that the two are not blurred: the fatty acid and the ester of that fatty acid are different test materials, and the fact that one looked comedolytic in humans is not a finding about the other, in either direction. It does not clear isopropyl linoleate — an untested material is untested, not exonerated — and it does not condemn it either. The assay itself has been contested for decades, and the objections cut toward a high grade as much as away from it. Frank asked in 1982 whether the rabbit ear predicts human acnegenicity at all. Draelos and DiNardo, in 2006, tested finished products on human backs and found that isolated ingredient scores did not transfer intact to the formulas they ended up in. A 2025 review in JAAD Reviews found that no standardised comedogenicity test exists and that the label "non-comedogenic" is unregulated. Those cautions apply to isopropyl linoleate's 4-and-4-5 exactly as much as to any reassuring number on this site.

Where you’ll see it

On a label it appears as Isopropyl Linoleate. It is used as an emollient and skin-conditioning agent in leave-on skincare, colour cosmetics and hair products, where a light, non-greasy slip is wanted. We have not audited its market share, and label position is not a dose, so treat that as the categories it suits rather than a measured prevalence. The Cosmetic Ingredient Review's safety assessment of the alkyl esters covers isopropyl linoleate and judged the group safe as used at the concentrations it reviewed; that is a judgement about toxicity, irritation and sensitisation, not about follicular plugging, and the two questions are separate. The neighbour to keep separate is the fatty acid itself. "Isopropyl Linoleate" on a label is the isopropyl ester; "Linoleic Acid" is the free acid, a different ingredient with a different entry and a different evidence base. They read similarly and are chemically related, but the rabbit assays above tested the ester.

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 of nearly every comedogenic number in circulation, read off a render of the journal scan rather than a list quoting it. Method: ingredient at roughly 10% in propylene glycol, 1 mL to the inner ear of three New Zealand albino rabbits, five days a week for two weeks, follicular keratosis scored under a micrometer — three animals, a rabbit ear, not a human face. Its Table I prints this ester as "Isopropyl linolate" (an older spelling of isopropyl linoleate) at a comedogenicity grade of 4 on a 0-to-5 scale, with no asterisk. Fulton's own key: 0 to 1 "not considered significant," 2 to 3 "borderline," 4 to 5 "considered positive." The same paper DEFINES grade 5 by isopropyl myristate — which sits at 5 in the table — so that sibling's famous 5 is the scale's calibration point rather than an independent reading, whereas this 4 is a graded result. Fulton called his survey "not at all definitive but simply designed to stimulate research." Consumer lists print a 4 for this ester as well; we did not trace which document each of them took it from, and a number that matches is not proof of copying, so we do not present them as further corroboration and we do not assert a chain we did not follow.
  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-to-5 scale, six years before Fulton and in a different laboratory — not a republisher of him. Model: rabbit ear canal, three rabbits, material applied undiluted unless stated, fourteen applications, microscopic grading. It scores isopropyl linoleate 4-5. Cited as the genuine second reading this page rests on: a different lab, testing the same named ester, also placed it in the positive band. Its limit is the same as Fulton's — a rabbit ear, not a human face, and the material tested neat rather than at an in-use concentration. Morris and Kwan are also on record contradicting Fulton on other materials, so the agreement here is not two labs that always agree.
  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, read in full from a print copy and transcribed in this repository. Cited for a negative, and only a negative: its Table I has NO row for this ester, under either spelling, so it neither corroborates nor contradicts the 1989 reading, and the absence is not a zero. Method: two New Zealand albino rabbits per test, the ingredient applied to one ear daily for two weeks with the other ear as control. Its threshold key also differs from 1989's — 1984 treats a grade of 3 or above as positive, where 1989 calls 2 to 3 borderline and reserves positive for 4 to 5 — which is why a number from one paper cannot be read against the other without carrying each key. The related ester rows it does print are not transferable to this one.
  4. Cosmetic Ingredient Review. "Amended Safety Assessment of Alkyl Esters as Used in Cosmetics." An expert-panel safety assessment covering isopropyl linoleate among the alkyl esters, cited for one narrow thing: it establishes the ingredient as a cosmetic emollient and skin-conditioning agent that the panel judged safe as used at the concentrations reviewed. A safety assessment weighs toxicity, irritation and sensitisation — not follicular plugging — so it is not evidence for or against a comedogenic rating, and we do not use it as one. Cited via CIR's ingredient record rather than a specific tentative or final PDF; the alkyl-esters assessment exists in more than one document state and we do not want to attribute the wrong one. We make no claim here about how far this ester penetrates skin: the dermal-penetration data in the alkyl-esters package we could retrieve is for a different ester, and a predicted penetration is not a measured one.
  5. Letawe C, Boone M, Piérard GE. "Digital image analysis of the effect of topically applied linoleic acid on acne microcomedones." Clin Exp Dermatol 23(2):56-58 (1998) A small double-blind, placebo-controlled, randomised crossover study in humans with mild acne, measuring microcomedones by digital image analysis of cyanoacrylate follicular biopsies. It reported roughly a 25% reduction in microcomedone size over one month with no change at placebo sites, and concluded that topical linoleic acid might act as a comedolytic. Cited ONLY for a material-identity contrast, and used as evidence for nothing about this page's ingredient: it tested FREE LINOLEIC ACID, not the isopropyl ester. The free fatty acid looking comedolytic in humans is not a finding about isopropyl linoleate, in either direction — they are different test materials, and blurring them is precisely the error this site exists to catch.
  6. Draelos ZD, DiNardo JC. "A re-evaluation of the comedogenicity concept." J Am Acad Dermatol 54:507-512 (2006) A "Current Issues and Opinion" piece in JAAD that tested finished products on human upper backs and found products testing non-comedogenic despite containing ingredients the rabbit assay had scored comedogenic. Cited because it cuts against a high rabbit-ear grade as much as a low one: it is evidence that an isolated ingredient's score does not transfer intact to the formula it ends up in. It is not a same-substance rabbit-versus-human validation, and we do not present it as one.
  7. "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 onward. It is a synthesis of the legacy literature, not a new measurement, and independent of Fulton only in authorship, since the corpus it surveys includes his. Cited for the field-wide caveat that no standardised comedogenicity test exists and that "non-comedogenic" is an unregulated label — the caution that governs every number on this page, the alarming ones and the reassuring ones alike.
  8. 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 both of this page's numbers come from. Cited for the caveat, which applies symmetrically: the model's weaknesses undercut a high 4 exactly as much as they would undercut a reassuring 0.

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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