Algin

We rate Algin (sodium alginate) Caution at Low confidence — a precaution and not a measurement: it is a brown-seaweed thickener that sits on acne-clinic avoid-lists, and the comedogenic 4 that follows it around traces to no assay we can find.

What it is

A seaweed thickener. The Cosmetic Ingredient Review's 2015 final report on polysaccharide gums puts it plainly: "Algin is the sodium salt of Alginic Acid. Alginic Acid is the carbohydrate obtained by the alkaline extraction of various species of brown seaweed, Phaeophyceae." Chemically it is a linear polymer of mannuronic and guluronic acid — a long carbohydrate chain, closer to a food gum than to anything on the fatty-acid or ester rows that most comedogenic scores come from. On a label it reads Algin, or its synonym Sodium Alginate. What it is doing in a formula is thickening it. CIR lists its cosmetic function as a viscosity increasing agent, and reports it at concentrations up to 50% in paste masks and mud packs and as low as 0.001% in aerosol products. The same CIR report lists alginic acid and the ammonium, calcium and potassium alginates as GRAS-affirmed direct food additives — the same family of gel-formers behind alginate face masks, dental impression material and the thickened texture of many foods. Its close relatives on a label are alginic acid, calcium alginate, potassium alginate and propylene glycol alginate, and it sits in the same seaweed cluster as carrageenan (from red algae) and algae extract.

Why we rate it Caution

We rate it Caution at Low confidence, on the evidence tier we call uncited-list — the same tier, and the same basis, as algae extract. It is worth starting with the number, because the number is the reason anyone looks this ingredient up. Search "sodium alginate comedogenic" and you will be told it scores 4 out of 5 — "fairly high" — and that acne-prone skin should avoid it. We went looking for where that 4 comes from. We rendered Fulton's 1989 Table I and read all 220 rows by eye: there is no algin row in it, no alginic acid row, no alginate row, and no seaweed or kelp row of any kind. Morris and Kwan's 1983 assay — the other rabbit-ear study on the same 0 to 5 scale, six years earlier and in a different laboratory, whose 32 rows we hold in full — has no alginate row either. So this is not the coconut oil case, where the 4 belongs to coconut butter, or the lanolin case, where it belongs to the alcohol derivative. There is no neighbouring row to have misread. The 4 is attached to a material that no assay in the corpus we searched ever put on a bench. What actually stands behind the Caution is the thing that stands behind algae extract's: the pore-clogging avoid-lists that acne-focused estheticians keep. Face Reality's list, which our data cites, names Algin alongside Algae Extract, Carrageenan, Chlorella, Spirulina, Seaweed and Plankton. It is an alphabetical column of ingredient names on a brand's own site, published with no method, no scores, no patient counts and no reference to any study, next to products sold as free of the things on it. That is an opinion with a commercial interest attached, and we read it as one. The rationale usually offered for the whole seaweed cluster is iodine — that algae is iodine-rich, iodine is excreted through the follicle, and so it provokes comedones. We take that argument apart at length on the algae extract page and will not re-run it here; the short version is that iodine-induced eruptions are a neutrophilic hypersensitivity reaction rather than a plugged follicle, and the exposures that produce them are systemic doses of iodide, not a purified carbohydrate used to thicken a cream. It is the wrong lesion, and algin is a refined polysaccharide salt rather than whole kelp tissue. So why hold the Caution at all? Because practitioners who treat acne every day put this ingredient on a list, and we are not going to overrule people who see clogged skin merely because they did not publish. But an unpublished opinion is an opinion. We cannot tell you how many faces it rests on, because nobody who repeats it has said. The confidence is Low, the tier is literally called uncited-list, and that is the whole of what the rating is.

What the evidence doesn’t tell you

We can find no comedogenicity measurement of algin, and we want to be exact about the shape of that absence rather than inflate it in either direction. What we checked: Fulton 1989 (no row), Morris and Kwan 1983 (no row), and the rest of the numeric corpus rendered at /how-we-decide, none of which assays it. That is the boundary of what we looked at. It is not a census of every proprietary, non-English or unpublished assay that might exist somewhere; a search is not a proof of a negative, and we are not going to dress one up as the other. The CIR's 2015 final report is a safety assessment, not a comedogenicity study: the words "comedogenic", "acne", "pore" and "follicle" do not appear anywhere in it. It is cited here for what algin IS and how much of it goes into a product, and for nothing about pores. Safety is not comedogenicity, and we are not going to borrow one to stand in for the other. The same report notes that the substantial molecular size of these polysaccharides suggests skin penetration would be limited — but penetration through skin and plugging of a follicle are different endpoints, that sentence is about the former, and it is not evidence about comedones. An unmeasured risk is not a measured safety. One thing does cut cleaner here than on the algae extract page. "Algae extract" is a retired label covering organisms from a freshwater bacterium to a thirty-metre kelp, so a single comedogenic verdict across it is close to meaningless. Algin is one named substance — the sodium salt of alginic acid — so the material-identity problem is smaller. That is not a point in the ingredient's favour: a cleaner identity does not manufacture evidence that was never collected. It only means the absence is about one molecule instead of a kingdom of them. And "one molecule" is itself a simplification — commercial sodium alginate varies by molecular weight, mannuronic-to-guluronic ratio, viscosity grade, seaweed species, purity and residual ions.

Where you’ll see it

As a thickener and gel-former, most visibly in peel-off "alginate" masks, mud packs and clay treatments, and more quietly as a texture modifier in gels, creams, lotions and toothpaste. The CIR survey puts its highest cosmetic use — up to 50% — in paste masks and mud packs, which is unusual; most ingredients on this site appear well below 1%. Those are illustrative categories, not a measured prevalence: we have not audited the market, and where it sits on a label tells you nothing about the dose. It appears as Algin or Sodium Alginate, and its siblings — alginic acid, calcium alginate, potassium alginate, propylene glycol alginate — turn up on the same kinds of products. It sits in the seaweed cluster with carrageenan and algae extract; all three are on the same uncited avoid-list, and for all three we can find no assay.

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. Cosmetic Ingredient Review. "Safety Assessment of Polysaccharide Gums as Used in Cosmetics" — FINAL REPORT (October 22, 2015) A safety review of 106 polysaccharide gums, algin among them, by the Cosmetic Ingredient Review — an industry-funded panel convened by the cosmetics trade association (the Personal Care Products Council) — read off the PDF whose cover page reads "Status: Final Report. Release Date: October 22, 2015" — the final, not one of the comment-stage CIR drafts this site has been burned by before. Source of the identity on this page: algin is the sodium salt of alginic acid, extracted from brown seaweed (Phaeophyceae), a linear polymer of mannuronic and guluronic acid; its function is viscosity increasing; it is used up to 50% in paste masks and mud packs; and alginic acid and several alginates are GRAS food additives. It assesses safety, not comedogenicity — the words "comedogenic", "acne", "pore" and "follicle" do not appear in it — and we use it for nothing about pores.
2. 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 number in circulation, and cited here for an ABSENCE. Read off a high-resolution render of the journal scan, all 220 rows of Table I transcribed by eye. It contains no algin row, no alginic acid row, no alginate row, and no seaweed or kelp row of any kind. Method: ingredient at roughly 10% in propylene glycol, inner ear of three New Zealand albino rabbits, five days a week for two weeks, follicular keratosis scored 0 to 5. There is nothing in it to attach a 4 to.
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 to 5 scale, six years BEFORE Fulton 1989 and in a different laboratory — not a republisher of him, and it contradicts him in print on other materials. Cited here for what its 32 rows (seven lanolins, nine vegetable oils, eleven esters, five surfactants) do NOT contain: any alginate. The second of the two 0 to 5 assays we hold in full, and neither has ever scored this ingredient.
4. Face Reality Skincare pore-clogging ingredient list The entire basis of the Caution, and not a study. An uncited alphabetical list of ingredient names — Algae Extract, Algin, Carrageenan, Chlorella, Spirulina, Seaweed, Plankton among them — published on the site of a brand that sells products formulated without them. No method, no scores, no references, no patient counts. It tells you WHO flagged the ingredient. It does not tell you what they measured, and as far as anything public shows, the answer is nothing. This is the source the uncited-list evidence tier exists to describe honestly.
5. Acne Specialists — "Sodium Alginate Ingredient Added to Pore Cloggers List" An example of where a reader meets the number, not evidence for it. A clinic blog post that assigns sodium alginate a comedogenic 4 and repeats the seaweed-iodine rationale, with no assay, no citation and no method behind either. Cited so a reader who has seen the 4 can see what is printing it: a republisher of an avoid-list, not a measurement.
6. Hesseler MJ et al. "An acneiform eruption secondary to iododerma." JAAD Case Reports 4(5):468–470 (2018). PMID 29984285 The primary document behind the iodine paragraph, cited only for the point that carries over from the algae extract page: iododerma most commonly presents as an acneiform eruption, but the biopsy shows a neutrophilic hypersensitivity reaction — an ulcer with neutrophils and fibrinoid necrosis — not a comedone, and the documented routes are systemic (iodinated contrast, potassium iodide, amiodarone) or iodine applied to broken skin as an antiseptic. It says the pathophysiology is unknown and gives no dose threshold. The wrong lesion, from the wrong kind of exposure.

Others in the same family

Algae & seaweed 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 algae & seaweed as a family ›

• Algae Extract Caution Low
• Carrageenan Caution Low

Last reviewed 2026-07-12 · How we decide

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