Capric Acid

Capric acid is a medium-chain fatty acid that Fulton's 1989 rabbit-ear assay scored 2 out of 5 — a borderline result on the tester's own published key. An earlier rabbit study, Kanaar 1971, reported moderate follicular keratosis for the same acid but gave it no number at all.

What it is

A saturated medium-chain fatty acid, ten carbons long (C10), also called decanoic acid (CAS 334-48-5). It occurs naturally as a minor component of coconut and palm kernel oils. One thing about its identity matters before a number is read off it: free capric acid is not the same material as the C10 chains bound into caprylic/capric triglyceride, the lightweight emollient that carries a near-identical name and has its own separate entry. In that triglyceride the decanoic acid is esterified to glycerol and is not a free fatty acid at all. Fulton scored two mixed caprylate/caprate esters as materials of their own — his table prints "Glyceryl tricapylo/caprate" at 1 and "PG caprylate/caprate" at 2, on the same 0–5 scale — and neither row is a second reading of the free acid. Free capric acid is also a soap precursor: neutralised with sodium or potassium hydroxide it becomes a caprate salt, and cleansers are commonly built that way. What an ingredient list cannot tell you is whether that reaction happened, how completely, or how much free acid is left, so an alkali further down the label is not evidence about which material is in the jar. INCI function databases list capric acid's declared roles as cleansing, emulsifying and surfactant — declared functions, not evidence about pores.

Why we rate it Caution

We rate it Caution, at Low confidence. Two rabbit-ear records exist for this exact material, and only one of them is a number. Fulton 1989, in the Journal of the Society of Cosmetic Chemists — the paper the 0–5 scale everyone quotes comes from — diluted each ingredient to about 10% in propylene glycol, applied it to the inner ear of New Zealand albino rabbits, three rabbits per assay, and scored the follicles for keratosis. Capric acid scored 2 out of 5. On Fulton's own published key that is neither a clean result nor a positive one: he wrote that a grade of 0 to 1 "is not considered significant," that grade "2 to 3 is borderline," and that only "4 to 5" is "uniformally reproduceable and considered positive." A 2 is the bottom of borderline. The second record is eighteen years older and has no scale on it. Kanaar, in Dermatologica in 1971, applied fatty acids in the external ear canal of the rabbit and reported that caprinic acid — a historical synonym for capric acid, the same C10 decanoic acid, not a neighbouring chain length — induced "moderate inflammation and follicular keratosis," against marked effects from lauric and oleic acid and no distinct alterations from myristic, palmitic and stearic acid. We have read that abstract, not the paper: it carries no score, no scale, no concentration, no vehicle and no rabbit count, so "moderate" cannot be converted into a 2 or into anything else. What it does establish is that a different laboratory, well before Fulton and using a different site and method, also saw a follicular response to this acid. Read down Fulton's printed fatty-acid rows and the scores rise and then fall: caprylic (C8) 1, capric (C10) 2, lauric (C12) 4, myristic (C14) 3, palmitic (C16) 2, stearic (C18) 2–3*. Capric acid is a step above the near-inert C8 and well below the C12 peak, and lauric acid's 4 is the highest of his straight-chain fatty acid rows. The asterisk on stearic acid is Fulton's own, and means "results depend on source of raw material." That is what the table shows; the paper we hold offers no stated mechanism for the shape of it, and we are not going to supply one. Fulton also tested the same fatty acids in two further vehicles and printed the results in his Table III, where capric acid graded 2 in an organic solvent — his footnote for that column reads "ethyl ether or acetone," and the table does not say which was used here — and 3 in sunflower oil. That is the same paper and the same laboratory, so it is a vehicle comparison and not a second assay. The defensible reading is narrow: under Fulton's conditions the same named acid scored one grade higher in the oil than in the volatile solvent. Both readings sit inside his borderline band.

What the evidence doesn’t tell you

This is legacy animal evidence, and everything that limits the assays limits the rating. Both records are rabbit ears, not human faces, and Fulton was candid that his model's disadvantage is its extreme sensitivity — that not everything comedogenic in the rabbit is comedogenic in a person. We identified no study that has applied capric acid alone, at a known concentration, to human skin and counted comedones. Human work on free fatty acids of this chain length does exist, but it measures irritation: Kellum's 1968 series ran the free acids across the C2 to C16 range for relative irritancy, and erythema is not follicular plugging. We hold that citation, not its numbers. The two rabbit records also corroborate each other less than a count of two suggests. Kanaar's result is a word rather than a score, and his series parts company with Fulton's above C12: Kanaar found no distinct alterations from myristic, palmitic or stearic acid, where Fulton printed 3, 2 and 2–3*. Two laboratories agreeing that capric acid does something is not two laboratories agreeing on how much, and neither can be checked against the other on a common scale. Morris & Kwan 1983, the other rabbit study on the same 0–5 scale, has no capric acid row at all — its thirty-two rows are lanolins, vegetable oils, esters and surfactants — and there is no capric acid row in Fulton, Pay & Fulton 1984 either. The number is also not a fixed property of the molecule — Fulton's own Table III moves it with the vehicle — and it is borderline, which means the honest reading is uncertainty, not a verdict. Two papers bound how much a single borderline rabbit score can carry, though neither tested capric acid: Draelos and DiNardo, building a human upper-back model in 2006, argued that a comedogenic ingredient does not make a finished product comedogenic; and a 2025 review in JAAD Reviews found that no standardised comedogenicity test exists and that rabbit-ear results have been inconsistent in human skin.

Where you’ll see it

On an ingredient list it appears as Capric Acid. Its declared INCI functions are cleansing, emulsifying and surfactant, which is the job a formulator would give it — most often neutralised into its soap in a wash or a bar rather than left as the free acid. Those are declared functions and not a market survey we have run, and we did not find a figure for the concentration at which free capric acid is used in leave-on products. It should not be confused with caprylic/capric triglyceride, which shares much of the name, is a different material, and has its own entry — that is the far more familiar way a formula carries a C10 chain.

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 primary source for the 0–5 scale nearly every online list still uses, and the only document we hold that assigns free capric acid a comedogenic number. Rabbit-ear assay: about 10% of each ingredient in propylene glycol, applied to the inner ear of three New Zealand albino rabbits, follicles graded for keratosis. Capric acid is 2 in Table I; his own key calls 2 to 3 "borderline." Table III retests the fatty acids in two further vehicles and prints capric acid at 2 in an organic solvent (footnoted "ethyl ether or acetone") and 3 in sunflower oil — the same paper and the same laboratory, so a vehicle comparison rather than a replication. The scores read here were checked against a 400dpi transcription of the printed tables, not off a list that quotes them.
2. Kanaar P. "Follicular-keratogenic properties of fatty acids in the external ear canal of the rabbit." Dermatologica 142(1):14-22 (1971) An independent rabbit assay predating Fulton by eighteen years, and the only other document we have found that tested this exact material — under the historical name caprinic acid, a synonym for capric acid and decanoic acid, CAS 334-48-5. Its reported result is qualitative: lauric and oleic acid marked, caprinic acid "moderate inflammation and follicular keratosis," myristic, palmitic and stearic acid no distinct alterations. We have read the published abstract only; the paper is not open to us, PubMed indexes no abstract for it, and the abstract carries no numeric scale, concentration, vehicle or animal count. So it corroborates the direction of Fulton's result and cannot be placed on his 0–5 scale, and its readings above C12 disagree with his.
3. Draelos ZD, DiNardo JC. "A re-evaluation of the comedogenicity concept." J Am Acad Dermatol 54:507-512 (2006) A peer-reviewed "Current Issues" argument, not a rabbit-versus-human validation of capric acid; it did not test capric acid at all. The authors built a human upper-back occlusion model read by cyanoacrylate biopsy and concluded that finished products made with comedogenic ingredients are not necessarily comedogenic. Cited here only for the limit it places on reading an ingredient-level rabbit number, and disclosed as opinion-piece framing rather than a controlled trial.
4. "Comedogenicity in cosmeceuticals: A review of clinical relevance, regulatory gaps, and future directions." JAAD Reviews (2025) A recent peer-reviewed review of the field. It finds that no standardised comedogenicity test exists and that the rabbit-ear assay has produced inconsistent results in human skin. It makes no measurement of capric acid; it is cited for the state of the method, not for a score. A review synthesises the legacy assays rather than testing them again, so it is not independent evidence about this ingredient.
5. Kellum RE. "Acne vulgaris. Studies in pathogenesis: relative irritancy of free fatty acids from C2 to C16." Arch Dermatol 97(6):722-726 (1968) Cited for one thing only: to show that the human record on free fatty acids of this chain length is about irritancy, not comedones, so "no human comedogenicity study" is the accurate statement and "no human data" is not. It measures erythema, an endpoint that is not follicular plugging. PubMed indexes no abstract for it and we have not obtained the paper, so we report its citation and its stated scope and none of its results — in particular we do not attribute any C10 finding to it.
6. COSMILE Europe / SpecialChem INCI ingredient entries for Capric Acid Regulatory/identity references derived from the EU CosIng database. Used only for what capric acid is and its declared cosmetic functions (decanoic acid, CAS 334-48-5, from coconut and palm kernel oils; functions listed as cleansing, emulsifying and surfactant). These are declared functions and identity data, not comedogenicity evidence, and nothing here bears on pores.
7. CosDNA, acne.org and Banish comedogenic-ingredient lists Where most readers will already have met the 2. The figure they print matches Fulton's Table I row, which is the only published source of that number we could find; we have not traced each list's own sourcing, so what we can say is that they agree with Fulton rather than that they independently measured anything. None of them mentions Kanaar. They are named so a reader knows where the figure is available from; they add nothing to our confidence.

Others in the same family

Fatty acids 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 fatty acids as a family ›

• Lauric Acid Caution Low
• Myristic Acid Caution Low
• Palmitic Acid Caution Low
• Stearic Acid Caution Low

Last reviewed 2026-08-01 · How we decide

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