Isopropyl Myristate

The most notorious pore-clogging ingredient on the internet scores 5 out of 5 — but Fulton used it as the substance that DEFINES a 5, so that number is partly a definition rather than an independent reading. Two other rabbit assays tested it and also found it strongly comedogenic. Both human studies of it found little or nothing.

What it is

An ester of isopropyl alcohol and myristic acid. It is a thin, colourless, almost odourless liquid with a dry, non-greasy slip, and formulators reach for it for exactly that — it cuts the heaviness of an oil phase and leaves skin feeling clean rather than coated. It is also one of the most widely used penetration enhancers in both cosmetics and topical pharmacy. It partitions into the lipid layers of the stratum corneum and disorders them, which makes other molecules cross more easily; the CIR's alkyl ester review describes it plainly as "a non-polar penetration enhancer" that "is largely retained in the stratum corneum", and neutron diffraction and NMR work by Eichner and colleagues in 2017 mapped how it restructures model stratum corneum membranes. Those two jobs — light emollient, and carrier that opens the skin — are the whole story of this ingredient, and they are also the reason it ended up on every list.

Why we rate it Clogging

Start with the number, because the number is the strangest thing about this ingredient. Isopropyl myristate's legacy score is 5, the top of Fulton's scale, and that 5 is a tautology. Here is Fulton's own definition of the grade, in his own words: "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." Read it twice. Isopropyl myristate is the substance Fulton's top grade is DEFINED against. It is the calibration standard — the reference the scale was built on — and that has a consequence people miss: "as comedogenic as isopropyl myristate" is not an independent comparison when isopropyl myristate is what the comparison is made of. Every other 5 in this database means "it did what this molecule does." This molecule's 5 means "it did what it does." Now the correction, because we pushed that too far. We used to write that isopropyl myristate "did not score 5," that "its own number is not a measurement of anything," and that it had "never, in the strictest sense, been scored." That is wrong, and an external fact-check said so. Fulton applied the material under the same protocol as everything else, observed and described the response — large comedones, throughout the ear — and printed the result in his table: isopropyl myristate, 5 for comedogenicity, 3 for irritancy. A calibration standard is still a substance that was put on a rabbit and produced a large effect. What its use as the anchor limits is the INDEPENDENCE of the number, not the existence of the observation. The honest sentence is narrower than the one we liked, and it is the one that is true: Fulton's 5 is partly definitional, and the paper still documents a strong positive response. And it does not stand alone, which we also got wrong. Morris and Kwan tested the exact material in 1983 — isopropyl myristate at 50% in propylene glycol — in a different laboratory, on a 0–5 scale, and scored it 3 to 4. That is an independent rabbit result, it predates Fulton's famous table, and it was sitting in this project's own provenance file while the page claimed no such replication existed. Nguyen, Dang and Maibach then ran their own rabbit-ear assay in 2007 at a different institution again, and found isopropyl myristate positive among fourteen materials. So the rabbit evidence is not one lab's ruler. It is three laboratories, across three decades, agreeing. There is also a mechanism that hangs together: Fulton's hypothesis was that an ingredient must penetrate into the follicle to clog it, with a molecular weight between 200 and 300 in the danger zone. Isopropyl myristate weighs 270 and is sold, on purpose, as a penetration enhancer. Coherent — but coherence is not evidence, and every one of those three agreeing laboratories was looking at a rabbit's ear. That is why our confidence is Low rather than anything higher. Fulton had made the same call five years earlier, in a 1984 rabbit-ear paper in JAAD, where he named "isopropyl myristate and its analogs" as the lead ingredient offenders. That single sentence is where the whole ester family on this site descends from.

What the evidence doesn’t tell you

We can find no study of isopropyl myristate on a human face. Both human-model measurements of the ingredient point away from our rating, and it is worth stating exactly what they did and did not show. Lee, Kim, Jung and Ha, in 2015, applied 0.3 ml of isopropyl myristate under occlusion to a 16 cm² patch of upper back in eight Asian women, three times a week for four weeks, then took cyanoacrylate follicular biopsies. Microcomedone activity rose 63% from baseline. Untreated but occluded skin rose 54%. Petrolatum rose 55%. There was no significant difference between any of them — the occlusive tape appears to have done most of the work. Their conclusion was that isopropyl myristate is too weak a comedogen to serve as a positive control in human testing on Asian skin. Take that study at its true weight, which is not much: eight people, on the back rather than the face, in a population with far lower sebum output than the assay assumes (the authors measured 7.6 µg/cm² on the back against 45.7 on the forehead), published in a small and obscure journal, with no power calculation. It is thin evidence, and we would not overturn a rating on it. It is not, however, the only human test — we said it was, and Lee's own paper says otherwise on its own pages. Lee reports that Mills and Kligman, in the 1982 Archives of Dermatology paper that introduced the human comedogenicity model, applied 100% isopropyl myristate to five young African adults and found it none-to-weakly comedogenic. We have read that paper's abstract, which confirms the model — test substances occluded for a month on the upper backs of young black men with large follicles, follicular hyperkeratosis read by cyanoacrylate biopsy — but not its full text, so we are reporting Lee's account of its result rather than the result itself. The relevant point survives the caveat, and is now worse for the ingredient's reputation rather than better: there are TWO human studies of isopropyl myristate, forty-three years apart, and NEITHER found much. Nor has it been ignored by the field. In 2021, a double-blind randomised trial by Waranuch and colleagues explicitly declined to use isopropyl myristate as its positive control on precisely this concern, and reached for octyl palmitate instead — which raised microcomedones 365% in every subject, where isopropyl myristate had produced nothing distinguishable from sticky tape. That is the sentence to sit with: a working comedogenicity lab, in 2021, would not trust the ingredient the entire scale was built on to reliably clog a pore. One more thing from Mills and Kligman, and it is the sentence that ought to hang over this whole subject. In the abstract of the very paper that built the human assay, they wrote that "the rabbit model is more sensitive than the human," and concluded that substances weakly comedogenic in the rabbit "are probably safe for human use with the possible exception of acne-prone persons." The people who built both models are telling you the rabbit over-calls. And Draelos and DiNardo showed in 2006 that finished products built from comedogenic ingredients are not necessarily comedogenic; isopropyl myristate at the tail of a moisturiser's ingredient list is not the neat liquid a rabbit's ear received. The study that would settle this — isopropyl myristate at realistic concentration, in a real formula, on the faces of acne-prone people — has never been run. Everything on this page, and every legacy number on this site, is downstream of that absence.

Where you’ll see it

Everywhere, and often high on the list. The CIR's alkyl ester review recorded 1,149 reported uses in cosmetic formulations, second only to ethylhexyl palmitate among the 239 esters it covered, at concentrations up to 77.3% in hair grooming products, 76.6% in aerosol hair sprays and 23% in deodorants. On the face it turns up in moisturisers, cleansers, makeup and sunscreens, usually at far lower levels, and in topical pharmaceuticals as a vehicle chosen for its penetration-enhancing effect. It appears on a label as Isopropyl Myristate, sometimes abbreviated to IPM. It is also the anchor of the ester family as this site defines it — the analogs Fulton named alongside it in 1984, among them isopropyl palmitate, isopropyl isostearate, myristyl myristate, butyl stearate, decyl oleate and octyl palmitate, are flagged as a class largely because of their resemblance to this one molecule.

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 the score of 5. Method: ingredient diluted to 10% in propylene glycol, 1 ml applied daily to the inner ear of New Zealand albino rabbits, three rabbits per assay, five days a week for two weeks, follicles scored 0–5 for keratosis. Isopropyl myristate is listed at 5 for comedogenicity and 3 for irritancy — but the same paper defines grade 5 as comedones "similar to those induced by the application of our standard 'positive' testing agent, isopropyl myristate." It is the reference substance the scale was calibrated against, not an independent reading taken on it.
2. Fulton JE Jr, 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) The earlier Fulton rabbit-ear paper, from the same lab and the same model. It names "isopropyl myristate and its analogs" first among ingredient offenders, and lists the analogs by name. This is where the ester family as a category comes from. It is not independent corroboration of the 1989 paper; it is the same investigator, five years earlier.
3. Nguyen SH, Dang TP, Maibach HI. "Comedogenicity in rabbit: some cosmetic ingredients/vehicles." Cutan Ocul Toxicol 26:287–292 (2007) An independent replication — the SECOND, not the only one, which is what we used to claim. A different lab, quantifying the comedogenic potential of fourteen cosmetic materials in the rabbit external ear canal; isopropyl myristate was among the nine deemed positive. It corroborates Fulton on the rabbit — and only on the rabbit. It is the same animal model, carrying the same objection.
4. 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 independent rabbit result this page previously said did not exist — and it was in our own provenance file the whole time. A different laboratory, SIX YEARS BEFORE Fulton's famous table, on the same 0–5 scale: Isopropyl Myristate at 50% in propylene glycol, scored 3 to 4. Note the condition: 50% in propylene glycol, not Fulton's default, so it is not a like-for-like rerun. But it is a separate lab reaching a strongly positive result on the exact material, and it means Fulton's calibration standard is not the only thing holding this rating up.
5. Lee E, Kim N, Jung A, Ha J. "Isopropyl Myristate and Cocoa Butter are not Appropriate Positive Controls for Comedogenicity Assay in Asian Subjects." J Cosmo Trichol 2:1000102 (2015) One of TWO human measurements of this ingredient — we used to call it the only one, and Lee's own paper cites the other (Mills & Kligman 1982, five young African adults, 100% isopropyl myristate, none-to-weakly comedogenic). Eight Asian women, isopropyl myristate occluded on the upper back three times a week for four weeks, microcomedones counted by cyanoacrylate follicular biopsy. Result: +63% microcomedone activity against +54% for untreated but occluded skin — no significant difference. Cited here because it exists and because it disagrees with our own rating, not because it is strong. It is eight people, on the back, in a low-sebum population, in a minor journal with no power calculation. We report it as weak evidence pointing the other way, which is precisely what it is.
6. Waranuch N, Wisutthathum S, Tuanthai S, et al. "Safety assessment on comedogenicity of dermatological products containing d-alpha tocopheryl acetate in Asian subjects: A double-blind randomized controlled trial." Contemp Clin Trials Commun 23:100834 (2021) A peer-reviewed randomised trial that is not about isopropyl myristate, but tells us something about it anyway. Its authors chose octyl palmitate as their positive control specifically because "IPM may not be a good positive control for comedogenicity test in human studies" — a working comedogenicity lab, in 2021, declining to trust the ingredient the whole scale was built on. Octyl palmitate raised microcomedones 365% in every subject.
7. Mills OH Jr, Kligman AM. "A human model for assessing comedogenic substances." Arch Dermatol 118:903–905 (1982) The paper that established the human back assay, and the source of the caveat everyone quotes: "The rabbit model is more sensitive than the human. Substances that are weakly comedogenic in the rabbit are probably safe for human use with the possible exception of acne-prone persons." We cite the abstract, which we have read. We could not obtain the full text, so we do not repeat the specific isopropyl myristate finding that later authors attribute to it.
8. Draelos ZD, DiNardo JC. "A re-evaluation of the comedogenicity concept." J Am Acad Dermatol 54:507–512 (2006) Peer-reviewed rebuttal of the assumption underneath every comedogenic list — that a finished product containing a comedogenic raw material will itself be comedogenic. Six subjects, finished products, human back model. Conclusion: it will not necessarily be. This is the strongest published argument against reading our own number as a verdict on a product.
9. "Comedogenicity in cosmeceuticals: A review of clinical relevance, regulatory gaps, and future directions." JAAD Reviews (2025) Recent peer-reviewed review of the whole field, 1972 to 2025. Finds that the rabbit-ear assay guided the ratings but produced inconsistent results in human skin, that no standardised comedogenicity test exists, and that "non-comedogenic" is an unregulated label. 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.
10. Cosmetic Ingredient Review Expert Panel. "Amended Safety Assessment of Alkyl Esters as Used in Cosmetics" (tentative amended report, December 2012) Industry-funded but independently panelled safety review. Source of the usage data on this page — 1,149 reported cosmetic uses, up to 77.3% in hair grooming aids, 76.6% in aerosol hair sprays, 23% in deodorants — and of the description of isopropyl myristate as "a non-polar penetration enhancer" that is "largely retained in the stratum corneum". These are the figures we read in the report itself; an "up to 11%" leave-on figure we had previously carried turned out on checking to belong to oleyl linoleate, and has been dropped. On comedogenicity the review says only that the ingredient "produced comedogenic activity in rabbit ears", citing the same animal literature. It assesses safety, not pore-clogging, and it reports no human comedogenicity data.
11. Eichner A, Stahlberg S, Sonnenberger S, et al. "Influence of the penetration enhancer isopropyl myristate on stratum corneum lipid model membranes revealed by neutron diffraction and 2H NMR experiments." Biochim Biophys Acta Biomembr (2017) Biophysics, not dermatology. Neutron diffraction and solid-state NMR on model stratum corneum membranes, showing how isopropyl myristate inserts into and restructures the skin's lipid lamellae. Cited for mechanism only — it explains why the molecule crosses into skin, which is what Fulton believed a comedogen has to do. It does not measure comedones and cannot support a claim that it causes them.
12. acne.org comedogenic ingredient list Listed because it is where most readers will have met this ingredient, and because it is more careful than its reputation. It does not simply republish Fulton's 0–5 numbers: it compiles eleven studies — including Fulton, Mills and Kligman, Nguyen and Maibach, and Draelos — into a binary avoid list. It is still a compilation of the same rabbit-ear corpus, and it is not an independent measurement, but it is not a straight Fulton republisher either. CosDNA is the plainer case — it reprints Fulton's number 5 directly, with no method and no disclosure of where it came from.

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 ›

• Butyl Stearate Clogging Low
• Caprylic/Capric Triglyceride Clear Low
• Cetyl Acetate Clogging Low
• Cetyl Palmitate Clear Low
• Decyl Oleate Clogging Low
• Isocetyl Stearate Caution Low
• Isopropyl Isostearate Clogging Low
• Isopropyl Linoleate Clogging Low

Last reviewed 2026-06-23 · How we decide

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