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Ingredient ratings / Ricinus Communis (Castor) Seed Oil

Is castor oil comedogenic? What the pore-clogging tests found

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

Castor oil graded 1 out of 5 in Fulton's 1989 rabbit-ear test (10% in propylene glycol) and 0-1 out of 5 when Morris and Kwan applied it undiluted in 1983, so both published tests put it in the 'not significant' band. The caveat is that both are small rabbit-ear studies of the raw oil; no human comedogenicity test of castor oil turned up in the safety literature reviewed here.

Label name
Ricinus Communis (Castor) Seed Oil
Also listed as
castor oil, ricinus communis seed oil
Comedogenic grade
0–1 / 5 · Not significant (1)
Tests
  • Fulton 1989: comedogenic 1/5, irritancy 0/5 — rabbit ear, 10% in propylene glycol
  • Morris & Kwan 1983: comedogenic 0–1/5 — rabbit ear, undiluted

What the tests found

Castor oil is one of the few plant oils that two separate rabbit-ear studies tested and graded about the same.

Fulton 1989. In Fulton’s survey of skin care ingredients, castor oil was mixed 1:9 in propylene glycol (a 10% solution). One milliliter was spread on the inner ear of each of three albino rabbits once a day, five days a week, for two weeks. Follicle plugging was measured with a micrometer and on biopsy. Castor oil graded 1 out of 5 for comedogenicity and 0 for surface irritation [1]. Fulton’s scale treats 0–1 as “not significant,” 2–3 as borderline and 4–5 as positive. The test’s reference positive was isopropyl myristate, which reliably produced grade-5 comedones. Castor oil’s relatives scored in the same low range in Fulton’s table: hydrogenated castor oil 1, PEG-8 castor oil 1 (irritancy 1) and PEG-40 castor oil 0 [1].

Morris & Kwan 1983. This lab applied castor oil undiluted to the ear canals of three rabbits for 14 applications and graded follicles only under the microscope, against the untreated ear. Their sample, from the Baker Castor Oil Company, scored 0–1 [2]. The paper printed a range because the animals disagreed by one grade. Their Table III also gives castor oil’s main fatty acid as ricinoleic acid, at 87% of the triglyceride content. That makes it chemically unusual among the oils they tested, which were dominated by oleic or linoleic acid [2].

The agreement matters because the two labs used very different doses. Fulton diluted the oil to 10%, and Morris and Kwan applied it neat. Neither dose produced more than slight plugging.

Where the evidence is thin

  • Small, old animal studies. Each result rests on three rabbits, and both studies are from the 1980s. Morris and Kwan note that animals vary most “at the lower, less reactive end” of the scale, though rarely by more than one grade [2]. A 0–1 result is therefore less certain than it looks.
  • The rabbit ear over-reacts. Mills and Kligman, who built the human back test, found the rabbit model more sensitive than human skin. They concluded that substances only weakly comedogenic in rabbits are probably safe for human use, with acne-prone people as a possible exception [3]. That lowers the stakes of a grade of 1, but it isn’t a human result for castor oil.
  • No human comedogenicity data. The Cosmetic Ingredient Review (CIR) assessed castor oil in 2007 and re-reviewed it in 2025. Neither the 2007 abstract nor the 2025 re-review summary reports a comedogenicity test [4][5]. The human findings they do cover are about irritation and allergy. In clinical tests castor oil was not a significant irritant or sensitizer, but the CIR notes reactions in people with occupational skin disease [4]. The 2025 re-review adds a retrospective study of allergic contact cheilitis (lip inflammation) in patients exposed to castor oil in personal cosmetics, plus several case reports of people who patch-tested positive to castor oil, hydrogenated castor oil or ricinoleic acid [5].
  • Source still matters. Fulton marks the whole oils section of his table “results depend on source of raw material” [1]. The castor oil in a given product isn’t necessarily the oil that was tested.

Where it shows up, and how much

The CIR describes castor oil as working mainly as a skin-conditioning agent, emulsion stabilizer and surfactant [4]. Its use is concentrated in lip products:

  • Earlier data: 769 uses in 2002, and a highest reported concentration of 81%, in lipstick, in the 2004 survey [4][5].
  • 2023/2022 data (CIR 2025 re-review): used in 1,018 products, at 0.0002% to 77.8% [5]. By category:
    • lipsticks: 199 uses at 12.5–75%
    • moisturizing products: 105 uses at 0.01–77.8% (non-spray)
    • face and neck products: 40 uses at 12.7% (non-spray)
    • cleansing products: 49 uses at 0.005–10% [5]

At 75% in a lipstick, castor oil will usually be the first ingredient on the label. In a face cleanser at a few percent, it will sit much further down. Morris and Kwan’s undiluted test is far above the levels in most products, though the top lipsticks (75%) and moisturizers (77.8%) come closer. Fulton’s 10% is close to the maximums reported for face and neck products (12.7%) and cleansers (10%).

If you want to avoid it

On the published grades, castor oil is already in the lowest band of the oils in this dataset, so swapping it for another plant oil is unlikely to lower the rating. Ingredients with similar emollient roles and the same or lower published grades:

  • Sunflower oil: 0 (Fulton 1989). Fulton says it is “naturally less comedogenic” [1].
  • Safflower oil: 0 (Fulton 1989), though Morris & Kwan graded it 1–2 [1][2]
  • Squalane: 1 (Fulton 1989) [1]
  • Hydrogenated castor oil: 1 (Fulton 1989) [1]

Oils that sit much higher in these tables include avocado, soybean and corn oil (3) and cocoa butter (4) [1]. A label that lists castor oil first, as in many lipsticks, means a much larger dose than one that lists it near the end.

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. 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/
  4. Cosmetic Ingredient Review. Final report on the safety assessment of Ricinus Communis (Castor) Seed Oil, Hydrogenated Castor Oil, Glyceryl Ricinoleate, … and Octyldodecyl Ricinoleate. Int J Toxicol. 2007;26(Suppl 3):31-77. https://pubmed.ncbi.nlm.nih.gov/18080873/
  5. Fiume MM, Bergfeld WF, Belsito DV, et al. Re-Review Summary of Ricinus Communis (Castor) Seed Oil and Ricinoleates as Used in Cosmetics. Int J Toxicol. 2025;44(Suppl 3):117S-122S. https://cir-reports.cir-safety.org/view-attachment/?id=c0735ee2-5758-8d9e-b7cb-2727cfc28a8c (abstract: https://pubmed.ncbi.nlm.nih.gov/40932363/)

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.