Ascorbic Acid
Ascorbic acid — vitamin C — is rated Clear, and the rating is an inference, not a reading off a table. We identified no comedogenicity assay of ascorbic acid in the legacy corpus we hold or the searches we ran. Fulton's 1989 survey has no ascorbic acid row at all; its nearest entry is ascorbyl palmitate, a fat-soluble ester and a different molecule, scored 2 of 5 — borderline by Fulton's own key. The checkers that hand vitamin C a flat 0 are asserting, not reporting.
No assay we can find, and no comedogenic concern on record.
What it is
L-ascorbic acid is the water-soluble, biologically active form of vitamin C. In a formula it is used as an antioxidant, and in higher-concentration serums as a brightening active. It is also notoriously unstable — it oxidises in water and air — which is the reason a whole family of more stable, and often oil-soluble, derivatives has grown up alongside it: ascorbyl palmitate, ascorbyl tetraisopalmitate, sodium ascorbyl phosphate, magnesium ascorbyl phosphate, 3-O-ethyl ascorbic acid, ascorbyl glucoside. That family matters on this page, because the comedogenic question people ask about "vitamin C" frequently lands on one of those derivatives, which are different molecules with different solubility and, in one case, a different score. On a label, the ingredient this page is about is Ascorbic Acid or L-Ascorbic Acid.
Why we rate it Clear
We rate it Clear, at Low confidence, and the confidence is Low for a specific reason: we identified no assay behind the rating. Consumer checkers display a 0 for ascorbic acid, but this audit identified no primary assay supporting that value, and no measurement of the comedogenicity of ascorbic acid in the corpus we searched. It has no row in Fulton's 1989 rabbit-ear survey — the source of nearly every comedogenic number in circulation — and none in any of the other numeric legacy papers we hold. The rating is an inference from the absence of any concern on record, not a measurement, and the honest thing is to say that plainly rather than to dress the inference up as a finding. What Fulton's table does contain, in Section X, "Vitamins and herbs," is a row for ASCORBYL PALMITATE, scored 2. That is a different molecule. Ascorbyl palmitate is the fat-soluble ester of vitamin C — ascorbic acid with a palmitic-acid tail attached so that it will dissolve in the oil phase of a formula — and it is a separately rated ingredient here. By Fulton's own published key, a 2 is "borderline": not a clean result and not a positive one. It sits on the 0–5 rabbit-ear scale, produced by applying the material at roughly 10% in propylene glycol to the inner ear of three rabbits, which is the method behind every number in that table. None of that is a measurement of ascorbic acid. It is the nearest thing to one in the whole corpus, and it is not the same molecule. A live checker shows the substitution waiting to happen. Platinum Skin Care's widely copied comedogenic list prints "Ascorbic Acid — 0" one line above "Ascorbyl Palmitate — 2." The 0 has no study behind it; the 2 is Fulton's, and it belongs to the ester. Two entries, two molecules, one letter of difference in how carelessly they get read. The physicochemistry points the same way the rating does, and it belongs here as reasoning, not as evidence, because that is what it is. Water solubility distinguishes ascorbic acid from the lipophilic derivatives that share its name, and the follicular plug the rabbit-ear assay was built to detect is a lipid one — but solubility is not a validated predictor of follicular plugging, and we know of no study that established it as one. So the distinction is a reason to keep the molecules apart, not a reason to believe a result about one of them; and we have found no experiment that would turn it into one. We are not going to write that ascorbic acid cannot clog a pore. We are going to write that we have found nothing showing whether it does, and that there is no reason on record to think it does.
What the evidence doesn’t tell you
The rating rests on an absence, and an absence is a weaker thing than a result. We identified no comedogenicity study of ascorbic acid — no row in Fulton 1989 or Fulton 1984, none in Morris and Kwan's thirty-two materials, none among Nguyen's fourteen, and no human comedone count in the searches we ran. "No concern on record" is the true statement; "proven not to clog pores" is not, and we are not making it. That gap is the whole reason the confidence is Low rather than higher. Topical L-ascorbic acid has been studied in humans, but the published clinical work we found is about photoprotection, pigmentation and collagen — not pores — and none of it counted comedones, so none of it answers the question this site is about. The Cosmetic Ingredient Review's 2005 assessment concluded that the water-soluble vitamin C compounds are safe as used in cosmetics. That is a safety conclusion, reached from irritation, sensitisation and toxicity data; safety and comedogenicity are different questions, and a safety clearance is not a comedone count. We cite the report for what it is and not for a number it does not contain. There is a real phenomenon underneath the question, and it is worth stating precisely. People do report breakouts from "vitamin C" products. Those reports do not identify a cause: the products are formulated in widely varying bases — some in oils or silicones — and many use one of the oil-soluble derivatives rather than ascorbic acid at all, so the reports neither implicate ascorbic acid nor exclude it. A result about a product is not a result about a molecule, and there is no single "vitamin C" whose behaviour a breakout report describes. The one adjacent laboratory number that does exist, ascorbyl palmitate's borderline 2, belongs to that different, fat-soluble ester — and reading it across to ascorbic acid would be the exact material substitution this site exists to catch.
Where you’ll see it
Antioxidant and brightening serums, most often labelled Ascorbic Acid or L-Ascorbic Acid, and usually near the front of the ingredient list when a product is built around it. The derivatives — ascorbyl palmitate, sodium ascorbyl phosphate, magnesium ascorbyl phosphate, 3-O-ethyl ascorbic acid, ascorbyl glucoside, ascorbyl tetraisopalmitate — appear under their own names and are different molecules with their own solubility and, where one exists, their own score. A label that says only "Vitamin C," with no INCI name, is not telling you which of these you are holding. We are not going to read a dose off label position, because ordering rules make that unreliable and we have not audited where the ingredient typically sits.
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.
- Fulton JE. "Comedogenicity and irritancy of commonly used ingredients in skin care products." J Soc Cosmet Chem 40:321–333 (1989) The primary source of nearly every comedogenic score in circulation, read here off the 400dpi transcription of Table I held in this repository rather than via a list quoting it. It contains NO ascorbic acid row, in any table. Its nearest entry is "Ascorbyl palmitate — 2," in Section X, "Vitamins and herbs" — a different, fat-soluble molecule. Method: the ingredient diluted to roughly 10% in propylene glycol, applied to the inner ear of three New Zealand albino rabbits, follicles scored for keratosis on a 0–5 scale, where by Fulton's own key 2 is "borderline." Cited to establish two things: that this survey contains no measurement of ascorbic acid, and that the one nearby number is not this molecule's.
- 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 rabbit-ear survey, read in full off the journal scan: two New Zealand albino rabbits per test, one ear dosed daily for two weeks, the alternate ear as control, on a 0–5 scale whose key differs from the 1989 one — there, 1 to 2 is not significant and 3 or above is considered positive. Cited for an absence: it has no ascorbic acid row, and no ascorbyl palmitate row either.
- 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, six years before Fulton 1989 and on the same 0–5 scale: undiluted material unless stated, three rabbits, fourteen applications, microscopic grading. Its thirty-two materials are seven lanolins, nine vegetable oils, eleven esters and five surfactants. Cited for an absence: ascorbic acid is not among them. It neither confirms nor contradicts anything on this page.
- 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 0–4 scale; abstract read via EuropePMC, full text and per-material scores not read, so no number is carried from it. Cited for an absence: its fourteen named test materials are esters, fatty alcohols, a sulfate, cocoa butter, paraffin and petrolatum, and ascorbic acid is not among them.
- Elmore AR (Cosmetic Ingredient Review). "Final Report of the Safety Assessment of L-Ascorbic Acid, Calcium Ascorbate, Magnesium Ascorbate, Magnesium Ascorbyl Phosphate, Sodium Ascorbate, and Sodium Ascorbyl Phosphate as Used in Cosmetics." Int J Toxicol 24(Suppl 2):51–111 (2005) An expert-panel SAFETY review of the water-soluble vitamin C compounds, concluding they are safe as used in cosmetics. Cited for exactly that, and for the distinction it forces: a safety conclusion is drawn from irritation, sensitisation and systemic-toxicity data, not from follicular plugging, so it is not evidence of non-comedogenicity. We have the published conclusion and citation; the full text is paywalled, and we do not report figures from inside a document we have not read.
- Platinum Skin Care — "Comedogenic Ratings" ingredient list A consumer "pore-clogging" checker run by a skincare retailer, cited as an example of where a reader will actually meet these numbers — not as evidence. Its table prints "Ascorbic Acid — 0" directly above "Ascorbyl Palmitate — 2." The 0 carries no source, no scale note and no assay behind it; it is an assertion. The 2 is Fulton's rabbit-ear score, and it belongs to the ester on the line below, not to ascorbic acid. The two rows sitting adjacent is the material substitution this page exists to keep apart.
Others in the same family
Antioxidants behave similarly enough that the evidence for one is often wrongly read across to the others. These are its structural relatives, not a guess.
Last reviewed 2026-08-05 · How we decide