Porecelain

Flawless skin starts with the fine print.

Propylene Glycol Monostearate

Propylene glycol monostearate carries a comedogenic number from the rabbit ear, and the man who produced it published two of them - 0 to 3 on a 0 to 5 scale in 1989, and a flat 4 on the same scale in 1984 - which straddle the threshold his own papers set for a positive result.

Clogging Low confidence Legacy score 4 on a 0-5 scale · Fulton 1984 · low reliability

Fulton 1984 printed 4 of 5, positive under its key; Fulton 1989 printed 0-3.

Sources disagree: Fulton 1984 printed 4 of 5 (positive under its key, used as is); Fulton 1989 printed 0-3 of 5 (never positive under its key). The rating follows the 1984 positive.

What it is

Stearic acid esterified onto propylene glycol, used to build and hold an emulsion. On a label it is usually not called this at all - the INCI name is Propylene Glycol Stearate, and the EU's CosIng entry lists "propylene glycol monostearate" as a chemical synonym for it, with the reported functions skin conditioning and cleansing surfactant. The naming matters more than it sounds, because the material is not a monoester. The Cosmetic Ingredient Review's 1983 final report opens by defining it: "Propylene Glycol Stearates (PGS) are a mixture of the mono- and diesters of triple-pressed stearic acid and propylene glycol." The word "monostearate" describes the principal ester in a mixture, not the contents of the drum. A self-emulsifying grade exists alongside it, and CIR assessed the two together in one report. Fulton's table does not split them. That is worth noticing because elsewhere in the same table he did split a stearate that way - "Glyceryl stearate NSE" scores 1 and "Glyceryl stearate SE" scores 3, on adjacent rows - so the single undifferentiated row here covers a distinction he treated as material in a neighbouring family.

Why we rate it Clogging

We rate it Clogging, at Low confidence, and the rating rests on Fulton's 1984 reading of 4, which is positive under that paper's own stated key. The 1989 reading of 0-3 is recorded here as the conflicting one. The entire direct evidence is two rabbit-ear readings by the same investigator that do not agree. Start with material identity, because on this site that is usually where the number falls apart, and here it holds. Fulton's 1989 table prints the row as "PG monostearate" - an abbreviation, which is the kind of thing that gets misread into a neighbour. It has not been misread. Seven rows above it the same table prints "Propylene glycol" at 0, and the row immediately below is "Ethylene glycol monostearate" at 0, so the paper distinguishes the two glycols in adjacent lines. And Fulton's earlier paper prints the name in full: "Propylene glycol monostearate". There is a row for this material, in both papers, under this material's name. The 1989 reading. Fulton's survey in the Journal of the Society of Cosmetic Chemists scores PG monostearate 0-3 on a 0 to 5 scale. The method behind that number - the test material at roughly 10 percent in propylene glycol, 1 ml applied to the inner ear of New Zealand albino rabbits, three rabbits per assay, five days a week for two weeks, follicular keratosis measured with a micrometer. Note the vehicle: everything in that paper was dissolved in propylene glycol, including this. And Fulton's own key to his own scale, which almost nobody quotes: "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." A range running 0 to 3 therefore begins below his threshold for significance and ends at the top of borderline. On his 1989 terms it is not a positive result. The 1984 reading, which is not on any list we checked. Fulton, Pay and Fulton's earlier survey in the Journal of the American Academy of Dermatology scores "Propylene glycol monostearate" 4, in its Table I under "Miscellaneous ingredients", on the same 0 to 5 scale. Two rabbits per test there rather than three, the material applied daily for two weeks to one ear with the other as control. That paper sets a different bar in print - "a minimal grade of 1 to 2 is not considered significant. However, a grading score of 3 or above is uniformly reproducible and considered positive" - so a 4 is positive by 1984's key, and would also be positive by 1989's. One laboratory, five years apart, one grade above the top of its own later range and across the threshold. One printed difference between the two runs is worth setting down. The 1984 row carries no asterisk, and in that paper the asterisk marks the materials that were diluted, in mineral oil or in a 10 percent alcohol gel - so an unasterisked row was applied as is, undiluted, where the 1989 assay put its materials at roughly 10 percent in propylene glycol. That is a difference in protocol, and it is the likeliest place the divergence comes from. Neither paper says so, and we are not offering it as a proven cause. We are not going to tell you which reading is right, because we do not know, and neither paper says why the other differs. What we can say is that both exist, that the second one is not on any list we checked, and that the number in wide circulation for this ingredient comes in at least two shapes as a result. No other laboratory's reading turned up in the papers we hold. Morris and Kwan's 1983 rabbit-ear survey - the other major assay of the period, and the one that contradicts Fulton in print on other materials - has no row for it. What it does have is "Propylene Glycol Isostearate" at 3-4, a different fatty acid on the same glycol, and that number is not this ingredient's. Nguyen, Dang and Maibach's 2007 rabbit study does not list it among its test materials. We identified no assay of propylene glycol monostearate outside Fulton's two papers.

What the evidence doesn’t tell you

We identified no study that counted comedones on human skin after applying this ingredient. Every number on this page is from a rabbit's ear - at roughly 10 percent in propylene glycol in 1989 and undiluted in 1984, against no measured in-use concentration that we hold - and Draelos and DiNardo argued in 2006 that rabbit-ear results do not reliably transfer to human skin. Those objections are why we discount the 4s elsewhere on this site, and they apply here in both directions. We do not know what produced the 1989 spread. Fulton attaches one explanatory footnote to a section heading - "Results depend on source of raw material," on section VI, "Oils" - and this row is not in that section. Our transcription carries the printed range and the section footnotes; it does not carry a reason for a range on this row, and we are not going to invent one. A range that runs from "not significant" to the top of "borderline" is a wide reading, and what varied inside it is not recorded in anything we have read. The material tested is probably not the material in the jar, and that is not a rhetorical flourish - CIR's own definition is that this ingredient is a mono- and diester mixture of stearic acid and propylene glycol. Neither paper reports a supplier, a monoester fraction, or whether the sample was the self-emulsifying grade, for either reading. A 1961 method paper for determining the monoester content of non-self-emulsifying propylene glycol monostearate appears in CIR's own bibliography, which is a fair sign that the proportion varied between suppliers and that somebody needed to measure it. Safety data exists and it is not comedogenicity data. The CIR's 1983 final report concludes that propylene glycol stearates are safe as cosmetic ingredients in the present practices of use, and its abstract records no significant skin irritation at concentrations up to 55 percent, no sensitisation on formulations containing 2.5 percent, and negative photo-contact allergenicity tests on formulations containing 1.5 percent. Those are irritation, sensitisation and toxicity endpoints. The abstract records no comedone count and no follicular examination. Safety is not noncomedogenicity, and a person tolerating 55 percent of something without redness tells you nothing about what it does inside a follicle. There is a later CIR document and we did not use it. A 2014 re-review packet on propylene glycol esters restates the 1983 conclusions, and every page of it is stamped "Distributed for comment only -- do not cite or quote." We read it, took nothing from it, and cite the 1983 final report instead. It contains one sentence worth flagging precisely because it is the kind of thing that gets misattributed: a propylene glycol ester "was also classified as an insignificant comedogen in rabbits." That sentence is about Propylene Glycol Dicaprylate/Dicaprate. It is not about this ingredient. Finally, the two secondary lists we checked do not agree with each other. One prints "PG monostearate (0-3)" - Fulton's own abbreviation and Fulton's own range - and then files it in a column headed "Low Risk (0-1)". Another, an esthetician's information folio, places "Propylene glycol monostearate" under "moderately comedogenic (3-4)" with no number, no scale and no citation. Neither mentions the 1984 reading. We have not traced how either list was assembled and do not claim to know.

Where you’ll see it

An emulsifier and thickener, and on a label it is Propylene Glycol Stearate rather than the name at the top of this page. CIR reports it used in a wide variety of cosmetic products; CosIng lists its reported functions as skin conditioning and cleansing surfactant. We have not audited the market and offer no prevalence figure. Nearby on an ingredient list you may meet propylene glycol itself, which Fulton scored 0 in both papers and which we rate separately, and glyceryl stearate and glyceryl stearate SE, which are different esters with their own numbers.

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 source of the 0-3, and the paper nearly every circulating comedogenic number comes from. Design - test material at roughly 10% in propylene glycol, 1 ml applied to the inner ear of New Zealand albino rabbits, three rabbits per assay, five days a week for two weeks, follicular keratosis measured with a micrometer, graded 0 to 5. Read off a 400dpi render of the journal scan, all 220 rows transcribed by eye, because OCR drops the numeric columns. The row is "PG monostearate", printed 0-3. What it cannot support - Fulton calls the survey "not at all definitive but simply designed to stimulate research", warns the rabbit ear is so sensitive that "not everything that irritates this model will also irritate human skin", and defines 0-1 as not significant and 2-3 as borderline. One animal assay, one laboratory, no supplier or grade stated for the test material.
  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(1):96-105 (1984) Fulton's earlier survey, read in full off the journal scan. Its Table I, under "Miscellaneous ingredients", prints "Propylene glycol monostearate" and scores it 4 on a 0 to 5 scale - one grade above the top of the 1989 range. Design - two New Zealand albino rabbits per test, the material applied to the internal surface of one ear daily for two weeks with the alternate ear as control, borderline cases confirmed by microscopic biopsy. Read with its OWN key, which is not the 1989 key: here Fulton wrote that "1 to 2 is not considered significant" and "3 or above is uniformly reproducible and considered positive", so this reading is a positive. Cited as the second Fulton reading, and as the reason we have flagged our own rating for review.
  3. Cosmetic Ingredient Review. "Final Report on the Safety Assessment of Propylene Glycol Stearate and Propylene Glycol Stearate Self-Emulsifying." J Am Coll Toxicol 2(5):101-124 (1983) A final report, not a tentative or comment-stage draft - the document read here is the published journal version, free access, headed "Final Report on the Safety Assessment of..." in Journal of the American College of Toxicology volume 2, number 5. Industry-funded, independently panelled toxicological safety review. The source of the composition statement on this page, verbatim from its abstract: "Propylene Glycol Stearates (PGS) are a mixture of the mono- and diesters of triple-pressed stearic acid and propylene glycol." Also the source of the clinical figures quoted - no significant irritation up to 55%, no sensitisation at 2.5%, negative photo-contact allergenicity at 1.5% - and of the conclusion that these ingredients are safe as used. Its limitation, and the reason it is not support for or against the rating: its endpoints are toxicity, irritation and sensitisation. We read the abstract and reference list, not the full 24 pages, and the abstract records no comedone count and no follicular examination.
  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 other major rabbit-ear survey of the period, on the same 0 to 5 scale, three rabbits, 14 applications, microscopic grading, and the paper that contradicts Fulton in print on other materials. Cited for what it does NOT contain: its 32 rows cover lanolins, vegetable oils, esters and surfactants, and propylene glycol monostearate is not among them. It does contain "Propylene Glycol Isostearate" at 3-4 - a different fatty acid on the same glycol, and a number that does not belong to this ingredient. It is the paper that would most plausibly have broken the tie between Fulton's two readings, and it did not test the material.
  5. Nguyen SH, Dang TP, Maibach HI. "Comedogenicity in rabbit: some cosmetic ingredients/vehicles." Cutan Ocul Toxicol 26(4):287-292 (2007) A later rabbit-ear assay on a 0 to 4 scale, cited only for its absence of this ingredient. Its published material list runs to esters, fatty alcohols, cocoa butter, paraffin and sodium lauryl sulfate; propylene glycol monostearate is not in it. We carry no number from this paper and make no claim about what it would have found.
  6. Draelos ZD, DiNardo JC. "A re-evaluation of the comedogenicity concept." J Am Acad Dermatol 54(3):507-512 (2006) A "Current Issues and Opinion" piece, not a same-substance rabbit-versus-human validation study. It tested finished products on human upper backs and argues that an isolated ingredient's rabbit score says little about the formula it ends up in. Cited against the rating as much as for it: it is a reason the confidence here stays Low whichever Fulton reading you prefer.
  7. Cosmetic Ingredient Review. "Safety Assessment of Propylene Glycol Esters as Used in Cosmetics", re-review packet for Panel review, release date 18 August 2014 A comment-stage document, not a final report: its status line reads "Re-Review for Panel Review" and every page carries the footer "Distributed for comment only -- do not cite or quote." Listed here to record that we read it and took nothing from it, and to flag one sentence in it that is easy to misattribute - "Propylene Glycol Dicaprylate/Dicaprate was also classified as an insignificant comedogen in rabbits" is about a different propylene glycol ester, not about this one.
  8. Banish, "The Ultimate List of Pore Clogging Ingredients To Avoid" (consulted August 2026) A commercial acne-products site publishing an ingredient list, cited as an example of how this number reaches a reader rather than as evidence. It prints the entry as "PG monostearate (0-3)" - Fulton's own abbreviation and Fulton's own printed range - inside a table column headed "Low Risk (0-1)", so the value and the heading it sits under disagree. It carries no scale, no method and no per-row citation, and does not mention the 1984 reading. We have not traced how the list was compiled.
  9. Simonsons, "Comedogenic Ingredients", Information Folio Series, revised 5/17 A salon-distributed esthetician's handout, cited as an example of the other shape this number takes. It places "Propylene glycol monostearate" in a band headed "MODERATELY COMEDOGENIC (3-4)" with no number, no scale, no method, no denominator and no bibliography. It is an assertion someone typed, not a measurement, and we treat it as one.

Others in the same family

Emulsifiers 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 emulsifiers as a family ›

Last reviewed 2026-08-12 · How we decide

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