Porecelain

Flawless skin starts with the fine print.

Sodium PCA

Sodium PCA is rated Clear, and this is one of the pages where the reassuring number turns out to be real and attached to the correct material: Fulton's 1989 rabbit-ear table prints a row for "Sodium PCA" at 0 on his 0-to-5 scale, the salt itself, not a neighbouring molecule and not a fabrication — though a single rabbit-ear 0, sitting in the band Fulton himself called insignificant, is thin evidence, which is why the confidence is Low.

Clear Low confidence Legacy score 0 on a 0-5 scale · Fulton 1989 · low reliability

Fulton 1989 rabbit ear 0 of 5 — one reading, not a set of assays.

What it is

PCA is the cosmetic name for pyroglutamic acid, the cyclic lactam formed from glutamic acid. Sodium PCA is its sodium salt. The European Commission's CosIng inventory, which we hold locally and searched directly, lists it under CAS 28874-51-3 and EC 249-277-1, gives its chemical name as sodium 5-oxo-2-pyrrolidinecarboxylate, and records its declared cosmetic functions as antistatic, hair conditioning, humectant and skin conditioning. It is small, water-soluble and strongly hygroscopic, which is what a formulator is buying: it goes into the water phase of a formula as a humectant, not into the oil phase as an emollient. The free acid, PCA, and the calcium, magnesium and potassium salts are separate declared ingredients with their own INCI names. This page is filed under the sodium salt because the sodium salt is the material the primary table tested, and the number stays where the paper put it.

Why we rate it Clear

We rate sodium PCA Clear at Low confidence. The rating is not in dispute. The evidence under it is one reading, and the only other line on the question is a sentence in a document we could not open. The legacy number, and it is the right material. James Fulton's 1989 survey in the Journal of the Society of Cosmetic Chemists is the source of nearly every comedogenic score in circulation, and we read its Table I off a render of the journal scan rather than off a list quoting it. It prints a row reading "Sodium PCA" at a comedogenicity grade of 0 on his 0-to-5 scale. The row sits near the end of the table, among the salts and miscellaneous materials, between "Amoniomethylpropinate" and "Hydrolyzed animal protein" — both spellings as printed. It is outside Section VI, "Oils," so it does not inherit the section asterisk that qualifies every oil and butter row in the paper, and it carries no asterisk and no range of its own. On this site that combination is the exception. Most of the famous numbers turn out, on inspection, to belong to a different material than the one they are quoted against, or to trace to no measurement at all. Here the printed row and the ingredient are the same thing, and the printed number is 0. A 0 from this assay deserves exactly the scepticism we give a 4 from it. The method is the ingredient at roughly 10% in propylene glycol, 1 ml applied to the inner ear of three New Zealand albino rabbits, five days a week for two weeks, follicular keratosis measured under a micrometer. On Fulton's own published key, a grade of 0 to 1 "is not considered significant," so a 0 is the floor of the band he treated as noise rather than as a finding — it is the absence of a signal in a model he called "not at all definitive but simply designed to stimulate research." The other primary inventories we hold are silent on it. Fulton's earlier 1984 rabbit-ear paper, whose table we hold transcribed in full, has no PCA row of any kind. Morris and Kwan's 1983 assay tested 32 materials — seven lanolins, nine vegetable oils, eleven esters and five surfactants — and none of them is a PCA salt. Nguyen, Dang and Maibach's 2007 rabbit survey names its fourteen test materials in its abstract, and sodium PCA is not among them. Those absences are read off the tables and lists themselves rather than assumed, and what they mean is that the 1989 row stands with nothing beside it to confirm or contradict it. There is one further line on the question, and we are recording it as a document to obtain rather than as a second measurement. The Cosmetic Ingredient Review has assessed PCA and its salts twice — Andersen's final report in 1999, and Fiume and colleagues' reassessment in 2019, which added the calcium, magnesium and potassium salts. Summaries of both report that no evidence of comedogenicity was found for sodium PCA. We could not retrieve either document while writing this page: every attempt to fetch the CIR PDFs and the journal versions failed on our side, so what we have is indexed abstract text and not the report body. We therefore cannot tell you what model was used, at what concentration, in how many animals or people, against what endpoint, or which underlying contract report the sentence is summarising. A summarised absence of evidence, in a document we have not read, is not something this page will treat as corroboration.

What the evidence doesn’t tell you

We identified no human comedogenicity study of sodium PCA in the corpus we searched — no cyanoacrylate follicular biopsy, no occluded back application, no counted comedones on a person. The rating rests on one rabbit-ear reading and nothing more direct we could trace. The rabbit ear is the model this site discounts when it condemns an oil, and consistency requires discounting it here. A 0 from a contested, oversensitive model is weak evidence of a 0, and Fulton's own key puts 0 to 1 in the band he did not consider significant, which is a statement about the resolution of his method as much as about the material. Dose is not settled by anything we read. Fulton's protocol applies the test material at roughly 10% in propylene glycol. That is a laboratory condition, not a formulation, and a single grade at one concentration does not contain a dose-response curve. The CIR line cannot be weighed. We have the sentence and not the study: no model description, no concentration, no n, no scale, no endpoint definition, and no way to check whether the underlying report is one of the rabbit-ear assays already counted here or something else entirely. If it is a rabbit result, it is not independent of the method, only of the paper. Either way, a safety assessment is a safety document: CIR's conclusion is that PCA and sodium PCA are safe as used, with a caveat about products containing nitrosating agents, and safety and comedogenicity are different questions. This page does not borrow one as an answer to the other. The score belongs to the salt Fulton printed. PCA itself, and the calcium, magnesium and potassium salts, have no rows in anything we hold, and we have not promoted the sodium reading across to them. Nothing we found examined molecular weight, concentration in a finished product, or interaction with other ingredients, so we cannot say how any of those bear on the question. And a rating is a property of an ingredient, not of a product: a formula that pairs a humectant with heavy occlusives can still clog pores. The 0 here belongs to sodium PCA.

Where you’ll see it

On a label it appears as Sodium PCA. It is water-soluble and hygroscopic, so it is formulated into the water phase rather than the oil phase. CosIng records its declared functions as antistatic, hair conditioning, humectant and skin conditioning; that is a regulatory inventory of what the ingredient is registered to do, not a survey of which products it appears in or how much of it is in the bottle in front of you, and we did not obtain the CIR use-concentration tables that would answer that.

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 rabbit-ear survey nearly every comedogenic number in circulation descends from, read off a render of the journal scan rather than off a list quoting it. Method: ingredient at roughly 10% in propylene glycol, 1 ml to the inner ear of three New Zealand albino rabbits, five days a week for two weeks, follicular keratosis graded under a micrometer on a 0-to-5 scale. Its Table I prints a row reading "Sodium PCA" at 0, among the salts and miscellaneous materials at the end of the table, outside the asterisked "Oils" section, with no range and no asterisk. Fulton's own key: 0 to 1 "not considered significant." He described the survey as "not at all definitive." Cited as the one traceable comedogenicity datum for this exact material, and as the same contested assay this site discounts elsewhere — a reassuring 0 from it is as weak as a condemning 4.
  2. Fulton JE, 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 paper, on its own 0-5 scale with a different threshold key from the 1989 paper. We hold its Table I transcribed in full, so it is cited here for a verified absence rather than for a number: it contains no PCA row of any kind, and it therefore supports no rating of this ingredient in either direction.
  3. 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) An independent primary rabbit-ear assay on the same 0-5 scale, six years before Fulton 1989 and willing to contradict him in print. Its 32 test materials are seven lanolins, nine vegetable oils, eleven esters and five surfactants, and no PCA salt is among them. Cited for that verified absence, which is part of why the 1989 row stands alone.
  4. 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 comedogenicity survey on a 0-4 scale. We have read its abstract verbatim and not its full text; the abstract names its fourteen test materials, which are esters, two alcohols, cocoa butter, paraffin, sodium lauryl sulfate and petrolatum. Cited for what it does not contain: no PCA salt was tested, so no second reading of this material could have come from it.
  5. Andersen FA (ed). "Final Safety Assessment for PCA and Sodium PCA." Int J Toxicol 18(Suppl 2):25-34 (1999) A Cosmetic Ingredient Review expert-panel SAFETY assessment of PCA and its sodium salt. WE DID NOT READ THIS DOCUMENT. Every attempt to retrieve the journal version and the CIR PDF failed while this page was written, so what we hold is indexed abstract text reporting that sodium PCA was non-irritating at concentrations up to 50% and that no evidence of phototoxicity, sensitisation or comedogenicity was found, with a conclusion that PCA and sodium PCA are safe as used but should not be used in products containing nitrosating agents. Cited as a document to obtain, not as a measurement: we cannot state the model, concentration, n, endpoint or underlying report behind the comedogenicity clause, and a safety conclusion is not a comedogenicity finding in any case.
  6. Fiume MM, Bergfeld WF, Belsito DV, Hill RA, Klaassen CD, Liebler DC, Marks JG Jr, Shank RC, Slaga TJ, Snyder PW, Gill LJ, Heldreth B. "Safety Assessment of PCA (2-Pyrrolidone-5-Carboxylic Acid) and Its Salts as Used in Cosmetics." Int J Toxicol 38(2 Suppl):5S-11S (2019) The Cosmetic Ingredient Review's reassessment, which carries the 1999 conclusions forward and adds the calcium, magnesium and potassium salts of PCA. WE DID NOT READ THIS DOCUMENT EITHER — the same retrieval failure — so we hold only its indexed summary, which repeats that sodium PCA was non-comedogenic in rabbits. Cited for the existence and scope of the reassessment and as the second document to obtain. The sentence it is summarised as containing has no design, no n and no scale attached to it in anything we could read, and we are not treating it as a second measurement.
  7. European Commission, CosIng cosmetic ingredient database — entry for SODIUM PCA (CAS 28874-51-3, EC 249-277-1) The EU's regulatory inventory of declared cosmetic ingredients, held locally in this repository and searched directly. Cited only for identity and declared function: chemical name sodium 5-oxo-2-pyrrolidinecarboxylate, functions antistatic, hair conditioning, humectant and skin conditioning. It is an inventory, not a study — it records what an ingredient is registered to do, contains no comedogenicity data, and supports no claim about pores.

Others in the same family

Humectants 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 humectants as a family ›

Last reviewed 2026-08-20 · How we decide

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