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Is isopropyl myristate comedogenic? What the pore-clogging tests found

By Skinredients · Checked against the sources 2026-10-16

In the rabbit-ear assay, isopropyl myristate is the benchmark for a positive result: Fulton (1989) graded it 5/5 at 10% in propylene glycol, and Morris & Kwan (1983) graded a 50% dilution 3-4/5. The main dispute is concentration: Kligman (1996) reported that below about 15% it was not comedogenic in rabbit or human tests, while Fulton said he was not convinced lower concentrations are safe.

Label name
Isopropyl Myristate
Also listed as
ipm
Comedogenic grade
3–5 / 5 · Positive in the test (4–5)
Tests

What the tests found

Isopropyl myristate (IPM) has a special place in this literature. In James Fulton’s 1989 survey it was not just another test material: it was the lab’s standard “positive” agent. A grade of 5 in that paper is defined as large comedones throughout the ear, “similar to those induced by” isopropyl myristate. That means its 5/5 is partly a matter of definition. The scale’s top grade is anchored to this ingredient [1].

The test used three rabbits and a 10% solution in propylene glycol (method), with plugging measured by micrometer, by eye and under the microscope. IPM also scored 3/5 for surface irritation, which on Fulton’s scale means generalized scaling with redness. Fulton’s Figure 2 photographs an IPM-treated ear, notes that the ingredient “is also an irritant,” and sets it beside octyldodecyl stearoyl stearate as “a potential substitute” [1].

Fulton also offered a chemical explanation. Mid-chain fatty acids such as lauric and myristic acid cause follicular plugging. When one of them is esterified with a small- to mid-size alcohol, “the combination becomes more potent than the fatty acid itself.” His own table bears this out: myristic acid scored 3/5, and its isopropyl ester scored 5/5. He calls the related esters (myristyl myristate, isopropyl isostearate, butyl stearate, decyl oleate) “cousins of isopropyl myristate” and reports that all of them were comedogenic [1].

A second lab reached a similar result. At Revlon, Morris and Kwan (1983) tested a commercial grade (Wickenol 101) at 50% in propylene glycol and graded it 3-4/5, scoring by microscopy alone [2]. They called it “perhaps the most widely used cosmetic emollient ester.” The 1984 rabbit-ear paper from Fulton’s group names “isopropyl myristate and its analogs” first in its list of ingredient offenders [3]. A 2007 rabbit study from Maibach’s group lists it among the materials “deemed positive” [4].

Where the evidence disagrees

The disagreement here is about concentration, not about whether neat IPM clogs pores.

  • Earlier mild results. Morris and Kwan noted that their high grades conflicted with the mild grades Kligman and colleagues had reported for IPM in earlier rabbit work [2].
  • Kligman’s 1996 position. Writing later, Albert Kligman said that neat IPM is “definitely comedogenic.” He also said that undiluted IPM produced microcomedones on the foreheads of people with active acne over eight weeks. However, he argued that IPM concentrations in facial products are “generally well below 15%,” and that at that level it was not comedogenic in either the rabbit or the human model. All of these observations are marked “unpublished” [5].
  • Fulton’s earlier objection. Seven years before Kligman’s paper, Fulton (1989) had already disputed a similar claim (Lanzet 1986). He was “not convinced” that lower concentrations of the major offenders “can be safely used with no comedogenic consequences.” He also described human back skin as “relatively insensitive” [1]. His 10% test is below Kligman’s 15% line, yet it still produced a 5.
  • Why 10% may not stay 10%. Fulton chose propylene glycol because it “gradually evaporates and leaves a concentrate of the raw material to be tested” [1]. The dose sitting on the ear by the end of each day may therefore be stronger than the nominal 10%. That may help explain why the labs disagree.
  • Rabbit vs. human. Mills and Kligman found the rabbit ear more sensitive than human skin [6]. In a human back test of finished products, Draelos and DiNardo (2006) concluded that products containing “comedogenic” ingredients are not necessarily comedogenic themselves [7].

Where it shows up, and how much

The Cosmetic Ingredient Review (CIR) amended alkyl esters report (final, April 2013) recorded 1,182 reported uses of isopropyl myristate: 959 in leave-on products and 208 in rinse-off products [8]. Reported maximum concentrations were:

  • 77.3% in “other hair grooming aids”
  • 76.6% in aerosol hair sprays
  • up to 60% in products that contact skin
  • 0.9-31% in eye-area products
  • up to 23% in deodorants

The same report describes IPM as a non-polar penetration enhancer that is largely retained in the stratum corneum. Its summary of the earlier review notes that IPM “produced comedogenic activity in rabbit ears.” The Panel’s overall conclusion was “safe … when formulated to be non-irritating” [8].

So the CIR survey shows products that contact the skin are reported at up to 60%, well above the “below 15%” level Kligman described. Where IPM appears on a label is a rough guide to how much is present.

If you want to avoid it

Fulton named his own replacement for IPM, and the rest of his table adds a few more. As the reference positive, IPM is the ester every other result is measured against, so these 0/5 grades from the same 10% test are the furthest from it on his scale [1]:

  • Octyldodecyl stearoyl stearate: 0, irritation 0. This is the “potential substitute” in his Figure 2.
  • Diisopropyl adipate: 0, irritation 0, an isopropyl ester of a dicarboxylic acid rather than a fatty acid
  • Pentaerythrityl tetracaprylate/tetracaprate: 0, irritation 0
  • Glycol stearate (printed as “ethylene glycol monostearate”): 0, irritation 0

Each of these grades comes from a single lab and a single test, so they are a lower published grade, not proof that a product is free of comedones. The esters Fulton calls IPM’s “cousins” do not help as alternatives. Isopropyl palmitate (4/5), isopropyl isostearate (5/5) and myristyl myristate (5/5) all scored high in the same table [1].

Sources

  1. Fulton JE Jr. Comedogenicity and irritancy of commonly used ingredients in skin care products. J Soc Cosmet Chem. 1989;40(6):321-333. https://library.scconline.org/v040n06/13
  2. Morris WE, Kwan SC. Use of the rabbit ear model in evaluating the comedogenic potential of cosmetic ingredients. J Soc Cosmet Chem. 1983;34(5):215-225. https://library.scconline.org/v034n05/1
  3. Fulton JE Jr, Pay SR, Fulton JE 3rd. Comedogenicity of current therapeutic products, cosmetics, and ingredients in the rabbit ear. J Am Acad Dermatol. 1984;10(1):96-105. https://pubmed.ncbi.nlm.nih.gov/6229554/
  4. Nguyen SH, Dang TP, Maibach HI. Comedogenicity in rabbit: some cosmetic ingredients/vehicles. Cutan Ocul Toxicol. 2007;26(4):287-292. https://pubmed.ncbi.nlm.nih.gov/18058303/
  5. Kligman AM. Petrolatum is not comedogenic in rabbits or humans: a critical reappraisal of the rabbit ear assay and the concept of “acne cosmetica”. J Soc Cosmet Chem. 1996;47(1):41-48. https://library.scconline.org/v047n01/44
  6. Mills OH Jr, Kligman AM. A human model for assessing comedogenic substances. Arch Dermatol. 1982;118(11):903-905. https://pubmed.ncbi.nlm.nih.gov/7138047/
  7. Draelos ZD, DiNardo JC. A re-evaluation of the comedogenicity concept. J Am Acad Dermatol. 2006;54(3):507-512. https://pubmed.ncbi.nlm.nih.gov/16488305/
  8. Cosmetic Ingredient Review. Amended Safety Assessment of Alkyl Esters as Used in Cosmetics (Final Amended Report, April 12, 2013). https://www.cir-safety.org/sites/default/files/alkyle032013rep.pdf

Comedogenic grades describe single raw materials tested in a lab, usually on rabbit ears. They are a guide for acne-prone skin, not a prediction for any product or person, and this page is not medical advice. How the scale works.