Isocetyl Stearate

Isocetyl stearate is carried on the consumer charts as a 5, the top of the scale. No primary document we have read prints that number for this material. Fulton's 1989 table has no isocetyl stearate row at all; the one paper that printed a score for it, Morris and Kwan in 1983, printed 0-1 out of 5, undiluted. But a second rabbit paper, in 2007, deemed it comedogenic. Two assays disagree, and we rate it Caution — a hedge on that disagreement, not the reassuring Clear the one low reading alone would suggest.

What it is

An emollient ester. The Cosmetic Ingredient Review's 2015 alkyl esters assessment defines it as "the ester of isocetyl alcohol and stearic acid — the mixture of esters obtained from the reaction of branched-chain cetyl alcohols with stearic acid," CAS 25339-09-7, function skin-conditioning agent (emollient). Read that definition twice, because it decides what any score could even mean. Isocetyl stearate is not one molecule. It is a MIXTURE of esters, made from a mixture of branched sixteen-carbon alcohols, and the CIR's own wording says so. Which branched alcohols, in what proportion, is a property of the supplier's process, and no paper in the comedogenic literature states whose material it tested. Two laboratories testing "isocetyl stearate" thirty years apart were not necessarily testing the same jar.

Why we rate it Caution

We rate it Caution at Low confidence, because the two rabbit assays that tested it disagree. The reason is set out below. Start with the number a reader will have met. The consumer charts print isocetyl stearate as a 5 — Beneficial Botanicals' widely copied list gives it 5 out of 5, "High," in a table whose own preamble says only that the ratings "have been derived and compiled from various sources." No source is named. That chart is worth one more look before it is used for anything: on the same page it prints hexadecyl alcohol at 5, and hexadecyl alcohol is another name for cetyl alcohol, which Fulton's table prints at 2. What Fulton actually contains, for this material, is nothing. We have his Table I transcribed by eye off a 400dpi render, all 220 rows. There is no isocetyl stearate row in it. What is in it, close enough to be mistaken for it by anyone reading quickly, is Isocetyl alcohol at 4 — a different material, an alcohol rather than an ester — and Isopropyl isostearate at 5. We are not going to tell you the 5 was copied from either of those. We told a story like that once, about sodium chloride, and we had to retract it. Where the 5 came from is unknown to us, and unknown is what we will say. One paper whose score we have actually read printed one for this exact material. Morris and Kwan, 1983, in the Journal of the Society of Cosmetic Chemists — six years BEFORE Fulton's table, in a different laboratory, and a paper that contradicts Fulton in print on other materials. Rabbit ear canal, three rabbits, fourteen applications, microscopic grading. Their scale is 0-5, the same as Fulton's. Their row reads "Isocetyl Stearate — 0-1." By Fulton's published key a 0-1 "is not considered significant." And the exposure was high: Morris and Kwan tested their materials UNDILUTED unless the table says otherwise, and this row says otherwise about nothing. Neat isocetyl stearate on a rabbit's ear, scored 0-1, in the paper that scored isopropyl linoleate 4-5 and isopropyl isostearate 4. Now the paper that complicates it, which we went looking for precisely because the first two findings pointed so tidily one way. Nguyen, Dang and Maibach, "Comedogenicity in rabbit: some cosmetic ingredients/vehicles," Cutaneous and Ocular Toxicology 26(4):287-292 (2007). Rabbit external ear canal again. Its abstract lists the materials tested, 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, petrolatum. Then one sentence: "The first nine were deemed positive." Isocetyl stearate is the seventh name on that list. We have read that abstract and not the table behind it, so we carry no number from it and we will not invent one. What the abstract establishes is narrower than a score and still enough to matter: a primary rabbit-ear paper, twenty-four years after Morris and Kwan, put this material in its positive column. That is why the rating is Caution rather than Clear. Two rabbit assays, one reporting 0-1 out of 5 and the other reporting positive, are the same shape as sodium lauryl sulfate — where two assays flatly disagree and we rate Caution. The one number we have actually read is low, Morris and Kwan's 0-1, undiluted, which is why the rating is not Clogging; the later positive is why it is not Clear. An earlier note here attributed a score of "1-2 out of 4" to Nguyen and Maibach and called the material "close to inert"; we could support neither from anything we have read, and both are struck.

What the evidence doesn’t tell you

Everything here happened in a rabbit's ear, and nowhere else. We identified no human comedogenicity study of isocetyl stearate, and no study of any kind that counted comedones on a face after using it. The rabbit-ear assay itself has been under challenge since Frank asked in 1982 whether the model, in its then-present state, was prophetic of acnegenicity at all, and a 2025 review in JAAD Reviews found that no standardised comedogenicity test exists and that "non-comedogenic" is an unregulated label. Those objections cut against a 0-1 exactly as hard as against a 5. We have read one of the three papers that matter here in full table form, and it is not the one that disagrees with us. Morris and Kwan's row is transcribed and verified. Nguyen, Dang and Maibach's table is paywalled and we have only its abstract, so what we can say is that the paper deemed the material positive, not what it scored, at what concentration, or in what vehicle. Concentration is not a detail here: the same literature reports octyl palmitate at 3 undiluted and 1 at 50%, so a "positive" without a concentration attached is a result we cannot place next to Morris and Kwan's. Obtaining that table is the outstanding job on this page, and it is the document most likely to settle the rating. The material identity problem is not solved either, and it may not be solvable. Isocetyl stearate is a mixture of esters from a mixture of branched alcohols. Morris and Kwan name no supplier. Nguyen and colleagues, so far as their abstract goes, name none. Two rabbit papers reaching opposite conclusions about a supplier-dependent mixture is not obviously a contradiction at all — it may be two different materials with one INCI name — and we cannot tell from here which it is. The Cosmetic Ingredient Review has assessed this ingredient and concluded it is safe as used. That is not evidence for anything on this page. Safety is not comedogenicity, and in this instance the CIR's own record is explicit about the gap: its 2015 alkyl esters assessment, summarising the earlier stearate-ester report, records isocetyl stearate as "Safe as used (1985, reaffirmed 2005)" with the data column reading, in full, "No data were available." The safety conclusion was reached by read-across from structurally similar esters. There is no CIR comedogenicity result for this material.

Where you’ll see it

On a label it appears as Isocetyl Stearate. The CIR lists its function as skin-conditioning agent (emollient); we have not audited what fraction of the market uses it or at what concentration, and we are not going to tell you where it sits on an ingredient list, because position is not a dose. What is worth knowing is what it sits next to. Isocetyl ALCOHOL is a different ingredient, and Fulton scored it 4. Isopropyl isostearate is a different ingredient again, and both Fulton (5) and Morris and Kwan (4) scored it high. Three names on a label that a reader could easily flatten into one, carrying three different evidentiary situations — and only one of them, the one on this page, has a printed score anywhere near the bottom of the scale.

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. 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 only primary document we hold that prints a comedogenic score for isocetyl stearate, and the source of our rating. A rabbit-ear-canal assay: three rabbits, fourteen applications, microscopic (histological) grading, 0-5 scale, test materials UNDILUTED unless the table states a dilution. Its row reads "Isocetyl Stearate — 0-1". It is not a republisher of Fulton — it precedes him by six years and contradicts him in print elsewhere, writing that its own finding, and Kligman and Mills's, of the noncomedogenic activity of sodium lauryl sulfate "conflicts with the high scores published by Fulton et al." What it cannot support: it names no supplier and no lot for a material the CIR defines as a mixture, it is a rabbit and not a face, and it is one reading.
2. Nguyen SH, Dang TP, Maibach HI. "Comedogenicity in rabbit: some cosmetic ingredients/vehicles." Cutan Ocul Toxicol 26(4):287-292 (2007) The paper that cuts against our rating, cited here for that reason. A rabbit external-ear-canal assay on a 0-4 scale. WE HAVE READ ONLY ITS ABSTRACT — the full text is paywalled — and the abstract is what carries the finding: it lists fourteen test materials in order, with isocetyl stearate seventh, and states "The first nine were deemed positive." We therefore carry NO number from this paper: not a score, not a concentration, not a vehicle. What it establishes is that a second primary assay placed this material in its positive column, which is a concern on record and not an absence. Abstract read from the US EPA's HERO bibliographic record (HERO ID 1616835), which reproduces it in full, because the publisher's page is behind a challenge screen.
3. Fulton JE. "Comedogenicity and irritancy of commonly used ingredients in skin care products." J Soc Cosmet Chem 40:321-333 (1989) The 220-row rabbit-ear table nearly every circulating comedogenic number descends from, read here off a 400dpi render of the journal scan and transcribed row by row. Cited for what it does NOT contain: there is no isocetyl stearate row anywhere in it. It does contain Isocetyl alcohol (4) and Isopropyl isostearate (5) — different materials. Method: roughly 10% in propylene glycol, inner ear of three New Zealand albino rabbits, five days a week for two weeks. Fulton's own key: 0-1 "is not considered significant", 2-3 "borderline", 4-5 "considered positive". He called the survey "not at all definitive but simply designed to stimulate research."
4. Fiume MM, Heldreth BA, Bergfeld WF, et al. "Safety Assessment of Alkyl Esters as Used in Cosmetics." Int J Toxicol 34(Suppl 2):5S-69S (2015) The published, final journal version of the CIR's assessment of 237 alkyl esters — not a comment-stage draft; we read its cover page and its Table 2. Cited for two things, neither of which is a comedogenic score. First, the ingredient definition: "the ester of isocetyl alcohol and stearic acid — the mixture of esters obtained from the reaction of branched-chain cetyl alcohols with stearic acid" (CAS 25339-09-7), which is what makes the material supplier-dependent. Second, the data gap: its summary of the earlier stearate-ester report lists "Isocetyl stearate — Safe as used (1985, reaffirmed 2005) — No data were available", the safety conclusion having been reached by read-across from similar esters. A safety conclusion is not evidence of noncomedogenicity, and an expert panel finding no data is not the same as a study finding nothing.
5. Beneficial Botanicals — "Comedogenic Ratings" ingredient chart One of the uncited consumer charts where a reader actually meets the number: it prints "Isocetyl Stearate — 5", the top of its scale. It is not evidence, and it does not claim to be — its own preamble says the ratings "have been derived and compiled from various sources" and names none. Cited as the artefact under examination, and as a demonstration of how far these charts drift from the papers they gesture at: the same page prints hexadecyl alcohol — another name for cetyl alcohol — at 5, where Fulton's table prints cetyl alcohol at 2. We have not traced who copied what from whom, and we do not claim to have.
6. Acne.org — "What Is Comedogenicity, and What Ingredients Are Comedogenic?" Included because it is the most careful of the consumer-facing lists and it should be described accurately rather than lumped in with the charts. It does not simply republish Fulton: it states a rule (an ingredient is listed to avoid if two or more rabbit-ear assays or one human study found it comedogenic), cites eleven studies, and among them cites Nguyen, Dang and Maibach's chapter in the Handbook of Cosmetic Science and Technology, 3rd ed. (2009) — a 0-4-scale rabbit assay examining concentration and vehicle. Whether that chapter reports the same dataset as the 2007 journal paper is something we have not established, and we have read neither table.
7. 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 that applies symmetrically: the model's weaknesses undermine a reassuring 0-1 exactly as much as an alarming 5.

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
• Isopropyl Isostearate Clogging Low
• Isopropyl Linoleate Clogging Low
• Isopropyl Myristate Clogging Low

Last reviewed 2026-07-19 · How we decide

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