Esters
Two of the sixteen esters on this page are not ingredients the assays measured. They are the instruments the assays measure against: Fulton's 1989 paper defines its top grade, 5, as comedones "similar to those induced by the application of our standard 'positive' testing agent, isopropyl myristate", and the two published human back assays we hold that name a positive control both name octyl palmitate. This is the family that supplies the rulers, and the one time a ruler was checked against the other model, it did not survive the check.
What they are
An ester is what you get when an acid and an alcohol are joined and a molecule of water comes out. In cosmetics that usually means a fatty acid joined to an alcohol, and the point of doing it is feel. A free fatty acid is waxy and a free fatty alcohol is waxy; the ester of the two is often a thin, dry, fast-spreading liquid that thins an oil phase without leaving it greasy. Isopropyl myristate is myristic acid plus isopropyl alcohol. Decyl oleate is oleic acid plus decyl alcohol. Cetyl palmitate is palmitic acid plus cetyl alcohol, and is solid at room temperature, which is why it thickens rather than thins. SOME OF THE SIXTEEN STRAIN THE DEFINITION, and naming them is the page working rather than the page hedging. Caprylic/capric triglyceride is a TRIGLYCERIDE — three fatty acids on a glycerol backbone, which is what the pressed seed oils in our oil family are made of. We file it here because it is manufactured from selected C8 and C10 fatty acids rather than pressed out of a seed, and that is a decision about provenance, not chemistry. Cetyl palmitate and myristyl myristate are WAX ESTERS, a fatty acid on a long-chain fatty alcohol — the same class of molecule as jojoba, which we file under oil and which is not a triglyceride at all. Our families are a filing system for a reader holding a label, and where the filing system and the chemistry diverge, the chemistry is the thing to say out loud. ONE MEMBER TRAVELS UNDER TWO NAMES. Octyl palmitate and Ethylhexyl palmitate are two INCI names for one ester, the second having replaced the first in the nomenclature; Fulton's table prints Ethylhexyl palmitate and the human-assay literature prints octyl palmitate. What we can document is the renaming. Neither paper describes the material it tested beyond the name it used, so the equation rests on the nomenclature and not on anything either laboratory recorded — and we refused the equivalent equation on this site for almond oil, so we are not going to make it a proof here. AND FULTON'S SECTIONS ARE NOT OUR FAMILY. His 1984 table files isopropyl myristate, myristyl myristate, myristyl lactate, butyl stearate, isopropyl isostearate, isopropyl palmitate and decyl oleate under a heading reading "Surfactants and detergents", next to sodium lauryl sulfate and laureth-4 — neither of which is an ester and neither of which we file here. His 1989 table orders them differently again. When we say "this family" we mean the sixteen in the table below, and when we quote one of his headings we will say which paper it is from.
What the evidence actually says
Here is the thing this page exists to say. It is printed in the papers, twice, and it is not a matter of interpretation. FIRST RULER. Fulton's 1989 grade key, on page 322, defines the top of his scale by naming a substance: "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 one of the sixteen materials in the table below. So every 4 and every 5 in Fulton 1989 — for an oil, a lanolin, a pigment, anything — is a statement about how close the material came to one member of this family. It was not always so, and that is the part nobody quotes. His earlier 1984 paper defines the same grade against a different substance entirely: "Grade 5 is the presence of more severe comedones throughout the ear, similar to those induced by the application of coal tar." Between 1984 and 1989 the top of Fulton's scale stopped being coal tar and became this ester. The scale people quote as a fixed property of materials was recalibrated by its author, onto a cosmetic ingredient, in the five years between his two papers. One correction we owe in the same breath, because we have overreached on exactly this point before. A calibration standard is still a substance that was put on a rabbit's ear. Fulton's 1984 table prints Isopropyl myristate at 5 of 5 — measured, at that time, against coal tar — and his 1989 table prints 5 again, by which point the material was the reference. And a second laboratory tested it: Morris and Kwan, in 1983, scored Isopropyl Myristate (50% in propylene glycol) 3 to 4 on their own 0-to-5 scale. So the number is partly definitional and the observation behind it is real. Both sentences are true and the page needs both. SECOND RULER, AND IT IS IN THE OTHER MODEL. When comedogenicity is tested on people rather than rabbits — occlusive patches on the upper back, cyanoacrylate follicular biopsy, microcomedones counted — the reference substance is not always isopropyl myristate, and we can say exactly which studies chose what. Draelos and DiNardo used octyl palmitate as their positive control in 2006. Waranuch and colleagues used octyl palmitate in 2021 and published the counts: an octyl palmitate pad on the upper backs of fifteen men for four weeks took microcomedones from 6.1 plus or minus 0.6 at baseline to 27.3 plus or minus 4.7, an average change of 365.4 plus or minus 87.6 percent, with every analysed subject above a 50 percent increase. Lee and colleagues, in 2015, used isopropyl myristate and cocoa butter instead. Two studies choosing one ester and one study choosing another is not a protocol, and we will not write it as one. AND THE DISAGREEMENT RUNS IN ONE DIRECTION ONLY. Waranuch's team chose octyl palmitate specifically because, in their words, "IPM may not be a good positive control for comedogenicity test in human studies" — a working comedogenicity laboratory, in 2021, declining to trust the substance the rabbit scale is defined by. They had reason to. Lee, Kim, Jung and Ha, in 2015, occluded isopropyl myristate on the upper backs of eight women three times a week for four weeks and found microcomedone activity up 63 percent, against 54 percent for untreated but occluded skin: no meaningful difference, the tape doing the work. Their paper is titled "Isopropyl Myristate and Cocoa Butter are not Appropriate Positive Controls for Comedogenicity Assay in Asian Subjects". We identified no reverse experiment — no human study we found questions octyl palmitate, and no rabbit study we hold tests the two references against each other. The doubt is on one side. So the family-level fact is this. The rabbit scale is anchored on one ester; the human studies that name a positive control name a different one; and the human work that exists on the rabbit's anchor did not reproduce it. Those two members are also the only members for which we identified a comedone count on human skin at all — and they have one because they were the instrument, not because anyone set out to learn about them. We identified no comedone count on human skin for any of the other fourteen. Octyl palmitate does have a second rabbit reading: Morris and Kwan scored Octyl Palmitate 2 to 3 on their own 0-to-5 scale, undiluted, and we do not hold their grade key, so we translate that into no band at all. THIRD, AND IT IS HOW UNTESTED ESTERS ACQUIRED NUMBERS. Fulton's 1984 abstract names the offenders as a class: "isopropyl myristate and its analogs, such as isopropyl palmitate, isopropyl isostearate, butyl stearate, isostearyl neopentanoate, myristyl myristate, decyl oleate, octyl stearate, octyl palmitate or isocetyl stearate ..." Nine esters, condemned by resemblance to the reference material, and the sentence runs on past our excerpt to name a tenth, PPG-2 myristyl propionate. Three of those nine — octyl stearate, octyl palmitate and isocetyl stearate — have no numeric row in that paper's Table I. They were classified in prose, not measured. Two of our sixteen have no row in the 1989 table either, and the rows they get confused with are sitting right there. We have read all 220 rows off a 400dpi render of the journal scan. There is no isocetyl stearate row; there is an "Isocetyl alcohol" row at 4, which is a fatty alcohol we file in another family. There is no octyl stearate row; there is an "Octyldodecyl stearate" row at 0, a longer ester at the opposite end of the scale, and Fulton recommends that group as the substitute for isopropyl myristate. The one laboratory that did put isocetyl stearate on a rabbit — Morris and Kwan, undiluted — scored it 0 to 1. Two of the rows quoted in this paragraph are rows we hold no rating for: Octyldodecyl stearate at 0, and Isostearyl neopentanoate, which the 1984 abstract names and the 1989 table scores 3. Neither is a member of this family, and we report them as printed rows and rate neither. THE KEY, printed once for the whole family, because the charts that republish these numbers drop it. Fulton 1989: "a minimal grade of 0 to 1 is not considered significant. Grade 2 to 3 is borderline. However, a grade of 4 to 5 is uniformally reproduceable and considered positive." By that key, ten of our sixteen sit in his positive band — isopropyl myristate, isopropyl isostearate and myristyl myristate at 5, and cetyl acetate, ethylhexyl (octyl) palmitate, isopropyl linolate, isopropyl palmitate, isostearyl isostearate, myristyl lactate and stearyl heptanoate at 4. Butyl stearate and decyl oleate are at 3, which is BORDERLINE and is neither a warning nor an all-clear. Caprylic/capric triglyceride, printed under the name "Glyceryl tricapylo/caprate", is at 1, and cetyl palmitate is at 0 — the bottom of the same table. His 1984 key is not the same key: there, "a minimal grade of 1 to 2 is not considered significant" and "a grading score of 3 or above is uniformly reproducible and considered positive". A 3 is positive in the first paper and borderline in the second. Butyl stearate is 4 in 1984 and 3 in 1989. Decyl oleate is 3 in both, and the two papers disagree about what a 3 means. Neither number can be carried across without its own paper's key. LAST, THE TEST CONDITIONS, which in this family are printed inside the row name and then deleted. Morris and Kwan tested undiluted unless they said otherwise, and where they diluted they wrote it into the row: "Myristyl Myristate (50% in Mineral Oil)" scored 0 to 1 of 5. Fulton scored myristyl myristate 5 of 5 twice, and the two runs were not prepared the same way. The 1989 row comes from his routine method, roughly 10% in propylene glycol. The 1984 row carries no asterisk, and by that paper's own footnote an unasterisked material was used as is if it was a liquid or a soft solid, while the asterisked ones were diluted in mineral oil or made up as a 10% alcohol gel — so how the 1984 myristyl myristate was prepared is not resolved by anything the paper prints. What can be said is narrower than it looks: the same named material sits at opposite ends of the same scale, and the higher nominal concentration, in a different vehicle and protocol, returned the lower number. The tidy reconciliation is to call mineral oil the gentler vehicle, and we are not going to reach for it, because the only vehicle comparison Fulton actually printed runs the other way. His Table II grades one dye in four carriers: D&C red #36 scored 3 in mineral oil, 2 in pentaerythrital tetra capra/caprylate, 1 in propylene glycol and 0 in PEG 400. Mineral oil was the harshest of the four there, not the mildest. That is one dye and not an ester, so it settles nothing about myristyl myristate — which is the point. The vehicle plainly moves these numbers, and for myristyl myristate we found no such comparison in the corpus we searched, so neither we nor the charts can say which way it moves them.
What the evidence doesn’t tell you
None of the above says esters clog pores, and none of it says they do not. It says the numbers on this family are less transferable than a single-column chart makes them look, and it says so in both directions. ARITHMETIC IS NOT A MECHANISM, and the temptation here is strong enough to name. Exactly five rows in Fulton's 1989 table carry a bare 5, and three of them are in this family — and one of those three, isopropyl myristate, is the substance the grade itself is defined by. It would be easy, and it would sound clever, to conclude that esters score high BECAUSE the scale was calibrated on one. We do not know that, Fulton never says it, and the arithmetic does not support it either — the other two 5s are ethoxylates, and two of our own members sit at 1 and 0 in the same table. This site invented a molecular-weight argument once and had it refuted by arithmetic. We are reporting what is printed and stopping there. THE FAMILY FACT DOES NOT REACH EVERY MEMBER. It says nothing about cetyl palmitate, a wax ester Fulton scored 0, or caprylic/capric triglyceride at 1. It says nothing about stearyl heptanoate, cetyl acetate or isostearyl isostearate, each of which has a single Fulton reading and, as far as our reading goes, no second laboratory. The ruler observation is about how the SCALE was built, not about how any individual member behaves. THE HUMAN EVIDENCE IS TWO MEMBERS, AND IT IS THINNER THAN ITS ROLE SUGGESTS. Octyl palmitate's counts come from a study whose subject was an anti-acne formulation, not the ester; it appears as the positive control, at one strength, on backs rather than faces, in fifteen men. A positive control's job is to show that the subjects can form comedones at all, not to map a curve. Lee's isopropyl myristate result is eight women, on the back, in a population the authors measured as having roughly a sixth of the facial sebum output, published in a small journal with no power calculation — weak evidence pointing away from a rating we keep. We have not read the full text of Mills and Kligman's 1982 paper, which introduced the human back model and which later authors say also tested isopropyl myristate, so the absence we report above is bounded by what we read. EVERYTHING ELSE IS RABBIT EARS. Fulton's method: the ingredient at roughly 10% in propylene glycol, about 1 mL applied to the inner surface of one ear of a New Zealand albino rabbit, five days a week for two weeks, three rabbits per assay, the other ear as control, follicular keratosis measured with a micrometer. Morris and Kwan used the ear canal and mostly applied materials undiluted. Nguyen, Dang and Maibach ran a third rabbit assay in 2007 on a 0-to-4 scale and deemed nine of fourteen materials positive, several of them esters — we have read only the abstract, so we carry its classification and none of its numbers. Fulton called his own survey "not at all definitive but simply designed to stimulate research". A FAMILY-WIDE GENERALISATION IS THE KIND OF CLAIM THIS SITE EXISTS TO DISTRUST, including when we are the one making it. What is asserted here is bounded and checkable: two grade definitions printed in two papers, the positive controls named individually in three published human assays, one abstract naming nine esters as analogs, and the rows we transcribed. Everything past that is somebody's inference, and on this page it should be yours rather than ours. And the caveat that sits under every number on this site, and under this page's argument as hard as under the numbers it corrects: a 2025 review in JAAD Reviews, surveying the literature from 1972 onward, found that no standardised comedogenicity test exists and that "non-comedogenic" is an unregulated label. Unproven is not disproven, in either direction.
All 16 esters we rate
The legacy score is printed exactly as it appears in the paper, including the ranges, the asterisks and the parentheses. Those marks are not decoration. They are the paper telling you what its own number is worth.
Sources
- 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 400dpi render of the journal scan rather than off a list quoting it. A survey, not a controlled trial: ingredient at roughly 10% in propylene glycol, 1 mL daily to the inner ear of three New Zealand albino rabbits, five days a week for two weeks, follicular keratosis measured with a micrometer, graded 0-5. Three things on this page come out of it and out of nothing else: the grade key defining 5 as comedones "similar to those induced by the application of our standard 'positive' testing agent, isopropyl myristate"; the fourteen ester rows we quote, including the ABSENCE of any isocetyl stearate or octyl stearate row among all 220; and Table II, which grades one dye in four different carriers. Its author called it "not at all definitive but simply designed to stimulate research." One investigator, one laboratory.
- 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(1):96-105 (1984) Fulton's earlier rabbit-ear paper, two rabbits per test, on the same 0-5 scale, held here as a full transcription of Table I from a purchased print copy. It is the same investigator and the same model, so it is not independent corroboration in any sense but the date. It carries two things this page cannot get anywhere else: a grade-5 definition naming COAL TAR rather than isopropyl myristate, which is how we know the reference substance changed between his two papers; and an abstract naming "isopropyl myristate and its analogs" — nine esters — as the ingredient offenders, three of which (octyl stearate, octyl palmitate, isocetyl stearate) have no numeric row in the paper's own table. Its grade key also differs from 1989's: 1 to 2 not significant, 3 or above positive. A number from this paper cannot be laid beside a 1989 number without carrying both keys.
- 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 one genuinely independent rabbit-ear assay of the era: a different laboratory, six years before Fulton's famous table, on the same 0-5 scale, and willing to contradict him in print. Its Table III is printed rotated and returns nothing to OCR, so anyone who scraped this paper lost part of it. Eleven of its thirty-two rows are esters, and the page uses it for three of them: Isopropyl Myristate (50% in propylene glycol) at 3 to 4, Myristyl Myristate (50% in Mineral Oil) at 0 to 1, and Isocetyl Stearate, undiluted, at 0 to 1. Note what the row names carry: the concentration and the vehicle are printed as part of the material name, and both are lost the moment the number is copied into a chart. We do not hold this paper's own grade key, so we do not translate its numbers into "borderline" or "positive".
- Waranuch N, Phimnuan P, Yakaew 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 controlled human study whose SUBJECT is a test formulation, not an ester — cited for its positive-control arm, which is where this page's human numbers come from. Fifteen healthy men aged 20 to 45 with prominent follicular orifices; an octyl palmitate pad on the upper back for four weeks; comedones counted on epidermal biopsies under a stereomicroscope in the twelve subjects analysed. The control site went from 6.1 plus or minus 0.6 comedones at baseline to 27.3 plus or minus 4.7. Its authors state they chose octyl palmitate because "IPM may not be a good positive control for comedogenicity test in human studies", which is the sentence this page turns on. It provides no concentration series, no facial site, and no comparison against the rabbit grades.
- 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) The human measurement of the rabbit scale's own reference substance. Eight Asian women, isopropyl myristate occluded on the upper back three times a week for four weeks, microcomedones counted by cyanoacrylate follicular biopsy: activity up 63 percent against 54 percent for untreated but occluded skin, no significant difference. Cited because it disagrees with our own rating of that ingredient, not because it is strong — eight people, on the back, in a low-sebum population, in a minor journal with no power calculation. Weak evidence pointing the other way is what it is, and what we report it as.
- 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, not a same-substance rabbit-versus-human validation, and we have described it as the latter on other pages and been corrected for it. It ran a modified Mills and Kligman human assay on six people with prominent follicles, patching FINISHED PRODUCTS to the upper back three times weekly for four weeks and counting microcomedones by cyanoacrylate biopsy. Cited here for one narrow fact: octyl palmitate was the substance it trusted as its positive control. It publishes no comedone count for that control arm, and no grade for any isolated ingredient. Its headline finding — that finished products built from comedogenic raw materials frequently test non-comedogenic — cuts against reading any number on this page straight into a formula.
- Nguyen SH, Dang TP, Maibach HI. "Comedogenicity in rabbit: some cosmetic ingredients/vehicles." Cutan Ocul Toxicol 26:287-292 (2007) A third rabbit-ear assay, a different institution again, and the reason this family's evidence cannot be described as two papers. It is on a 0-TO-4 scale, not 0-5. We have read the abstract verbatim and not the table, so we carry its classification and none of its numbers: it names fourteen materials in order and states "the first nine were deemed positive", and seven of those first nine are esters in this family. A material's position in an abstract's list is not a score, and we do not print one for it.
- "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 the literature from 1972 onward. It is a synthesis of the legacy corpus rather than a new measurement, and independent of Fulton only in authorship, since the corpus it surveys includes him. Cited for the field-wide caveat that no standardised comedogenicity test exists and that "non-comedogenic" is an unregulated label — which applies to this page's argument about the rulers exactly as hard as to the numbers the argument qualifies.