Myristyl Myristate

Myristyl myristate carries a comedogenic 5 on the ester lists, and that number is real but it is not the whole record. Fulton's 1989 rabbit assay did score a material of this name a 5, his top grade. Morris and Kwan's 1983 assay scored a material of the same name 0 to 1, at a higher concentration, in a paper that says in print it disagrees with Fulton. The two labs that tested it give opposite answers, and the rating rests on the higher one.

What it is

A wax ester: the ester of myristyl alcohol and myristic acid, both fourteen-carbon chains. On a label it is Myristyl Myristate; its CAS number is 3234-85-3 and its molecular formula C28H56O2, a molecular weight of about 425. It is a white-to-yellowish waxy solid that melts at roughly 40 to 44 degrees Celsius — just above body temperature — which is why it is a solid in the jar and softens on the skin. It is insoluble in water and soluble in oils. Formulators use it as an emollient and a texture agent: it thickens and adds body to creams and lotions, helps stabilise emulsions, and leaves a dry, velvety, non-greasy feel rather than a slick one. The 1982 Cosmetic Ingredient Review assessment describes it and isopropyl myristate together, and it is worth keeping the two apart. They are different molecules — isopropyl myristate is the ester of isopropyl alcohol and myristic acid — and although both sit at Fulton's 5, only isopropyl myristate is the substance Fulton used to DEFINE a 5. Myristyl myristate's 5 is an ordinary reading on his scale, not the ruler.

Why we rate it Clogging

We rate it Clogging, at Low confidence, and the honest description of the evidence is that it is a disagreement between two rabbit assays, not a settled number. The number you will see first. On nearly every pore-clogging list myristyl myristate scores 5 out of 5, the top of the scale, and that number is not invented — unlike some of the fives that circulate on these lists, it traces to a printed row rather than to nothing at all. James Fulton's 1989 rabbit-ear survey in the Journal of the Society of Cosmetic Chemists — the table nearly every comedogenic score online descends from — lists "Myristyl myristate" at 5. By Fulton's own published key, which the lists quoting him leave out, a grade of 0 to 1 "is not considered significant," 2 to 3 is "borderline," and 4 to 5 is "uniformally reproduceable and considered positive." So on his terms a 5 is a firm positive. What produced that number. The rabbit-ear assay applies the ingredient at roughly 10% in propylene glycol to the inner ear of New Zealand albino rabbits, three rabbits per assay, five days a week for two weeks, and the follicles are then scored for keratosis under a micrometer. It is a screen for follicular plugging in a rabbit's ear, not a measurement on a human face, and Fulton himself called his survey "not at all definitive but simply designed to stimulate research." The paper the lists do not mention. Morris and Kwan, in the same journal six years earlier, in 1983, ran the rabbit-ear assay on thirty-two materials and scored myristyl myristate — at 50% in mineral oil — a 0 to 1. On the same 0 to 5 scale, that is Fulton's "not considered significant." It is not a near-miss: it is the opposite end of the scale from a 5, for the same named material. And Morris and Kwan were not quietly disagreeing. Their paper states, of a different surfactant, that their results "conflict with the high scores published by Fulton et al" — they knew their assay read lower than his and said so in print. The concentrations cut against the easy explanation. The obvious way to reconcile a 5 and a 0 to 1 is dose: perhaps Fulton used more. He did not. Fulton's general method was about 10%; Morris and Kwan's row is 50% in mineral oil — higher strength, not lower — and it still scored near zero. What differs is the vehicle — Fulton dissolved his in propylene glycol, Morris and Kwan theirs in mineral oil — and the two labs, and the exact ear method. So the disagreement is real and it is not simply a matter of strength; it may be as much about the assay as about the material. A third assay exists, and it leans the other way. Nguyen, Dang and Maibach's 2007 rabbit study in Cutaneous and Ocular Toxicology lists myristyl myristate eighth among its fourteen test materials and states in its abstract that "the first nine were deemed positive" — so its positive classification of this material is readable directly from the abstract. We have not obtained the full table, it uses a 0 to 4 scale rather than 0 to 5, and we do not carry a grade from it — a number we have not read is a number we do not print. We note it because it is a genuine data point and because leaving it out would tidy the picture in exactly the way this kind of page is supposed to resist. If it holds, the count is two rabbit assays reading myristyl myristate as comedogenic and one reading it as near-inert. So the record, stated plainly: one primary assay we have read scores it 5; one primary assay we have read scores it 0 to 1 and says it disagrees with the first; a third, whose table we have not read, classes it positive in its abstract. And Fulton's earlier 1984 survey, now read, scores it 5 too — so the two positive Fulton readings are five years apart, not one number repeated. The rating is Clogging, and it rests on those positive readings against one near-inert one. That is defensible, but it is not unanimous, and the "5" on the lists is doing more work than a contested reading can carry.

What the evidence doesn’t tell you

Everything numeric here rests on rabbits' ears. There is no human comedogenicity measurement of myristyl myristate that we have been able to find — no cyanoacrylate follicular biopsy study, no facial trial, no comedone count on a person. The three assays in play are all the rabbit-ear model, and that model has been contested for decades: Frank asked in 1982 whether it was "prophetic of acnegenicity" at all, Draelos and DiNardo in 2006 found finished products testing non-comedogenic despite containing ingredients the rabbit assay had scored comedogenic, and a 2025 review in JAAD Reviews found that no standardised comedogenicity test exists and that "non-comedogenic" is an unregulated label. None of that resolves the disagreement; it widens the error bars on both readings. The two assays we have read are not a clean replication of each other. Fulton tested at about 10% in propylene glycol; Morris and Kwan at 50% in mineral oil. Different concentration, different vehicle, different laboratory, different decade. That is precisely why their opposite results do not simply cancel to "somewhere in the middle" — we cannot tell how much of the gap is the material and how much is the method, and neither can anyone else from these two papers. The safety record is not a comedogenicity record, and it is easy to blur the two. The Cosmetic Ingredient Review concluded in 1982 that myristyl myristate is "safe as a cosmetic ingredient in the present practices of use," and the abstract we read reports it as nontoxic in acute animal tests, producing minimal to mild skin irritation, minimal eye irritation, and no sensitisation. That is a statement about toxicity, irritation and allergy. It is not a comedone count, and we could not read the report's full text to see whether it discusses pores at all. Safe and non-irritating is not the same claim as non-comedogenic, and we are not going to convert one into the other. The confidence is Low because the tier is a legacy rabbit-ear assay — in fact a conflict between two of them — with no human data behind it. A higher confidence would require the kind of evidence that does not exist here.

Where you’ll see it

Emollient and texture roles in leave-on products: creams and lotions, cleansing balms and sticks, lipsticks and lip balms, pressed powders and cream makeup, and hair conditioners, where its waxy, melts-near-skin character gives body without a greasy slip. It is also used to add slip to colour cosmetics. These are illustrative categories, not a measured prevalence — we have not audited the market, and we are not going to tell you where it tends to sit on an ingredient list, because label position is not a concentration and we do not have the figure. On a label it reads Myristyl Myristate, and it is worth not confusing it with the several other "myristate" esters near it, isopropyl myristate above all, which is a different molecule with its own entry.

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 the 5, and of nearly every comedogenic number in circulation. A rabbit-ear survey: ingredient at roughly 10% in propylene glycol, inner ear of New Zealand albino rabbits, three rabbits per assay, five days a week for two weeks, follicles scored for keratosis under a micrometer. Table I lists "Myristyl myristate" at 5, an ordinary reading on the scale — not the reference standard, which is isopropyl myristate. The score is read from the primary table (transcribed from the journal at 400dpi in this project's own data file), not from a list quoting it. Fulton's own key: 0–1 "not considered significant," 2–3 "borderline," 4–5 "considered positive." He described the survey as "not at all definitive."
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, six years BEFORE Fulton's famous table and on the same 0–5 scale — not a republisher of him, and one of the few legacy papers that openly disagrees with him in print. Three rabbits, ear canal, fourteen applications, microscopic grading. It scores "Myristyl Myristate (50% in Mineral Oil)" a 0 to 1 — Fulton's "not considered significant" — at five times the concentration Fulton used. Its discussion states that its determinations "conflict with the high scores published by Fulton et al." This is the paper the ester lists leave out, and it is the reason the 5 is contested rather than settled.
3. Cosmetic Ingredient Review. "Final Report on the Safety Assessment of Myristyl Myristate and Isopropyl Myristate." Int J Toxicol 1(4):55–80 (1982) An expert-panel safety assessment, cited for what it is and not for what it is not. It concludes the two esters are "safe as cosmetic ingredients in the present practices of use," and the abstract we were able to read reports myristyl myristate as nontoxic in acute oral and dermal animal tests, producing minimal to mild skin irritation, minimal eye irritation in rabbits, and no sensitisation in guinea pigs. It is a toxicity, irritation and sensitisation review, NOT a comedogenicity study, and we could not read its full text — only the abstract and reference list were accessible — so we make no claim about whether the body discusses pores. Safe and non-irritating is a different finding from non-comedogenic.
4. Nguyen SH, Dang TP, Maibach HI. "Comedogenicity in rabbit: some cosmetic ingredients/vehicles." Cutan Ocul Toxicol 26(4):287–292 (2007) A third rabbit-ear assay, on a 0–4 scale. Its abstract lists myristyl myristate eighth among fourteen test materials and states "the first nine were deemed positive," so the positive classification is readable from the abstract itself. WE HAVE NOT OBTAINED THE FULL TABLE, its scale is not Fulton's, and we do not carry a grade from it — a number we have not read is one we do not print. Listed so the third data point is visible rather than omitted, and flagged so nobody, including us later, mistakes it for a row we have read. Obtaining this paper is an open job, and its result bears directly on whether the rating should read Clogging or Caution.
5. "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. 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. Finds that no standardised comedogenicity test exists and that the label "non-comedogenic" is unregulated. Cited for the field-wide caveat that sits under every rating on this site, and with particular force under a number two rabbit labs cannot agree on.

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 2026-07-19 · How we decide

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