Evidence-based skin science

Niacinamide rebuilds your barrier1, fades dark spots slowly2, and does almost nothing for wrinkles3.

Three claims about one ingredient, each resting on a different quality of evidence. Most skincare writing blurs that together. We keep it visible.

Sources for this statement

Flip the switch. Each numbered claim in the headline will show the study behind it — what kind of study, how many people, which journal, and how much weight it can carry.

What the Stratum Grade means

Every claim and every ingredient on this site carries one of four grades. Here is exactly what each one is telling you — and a longer explainer on how we get there.

Latest articles

Long reads on ingredients, treatments and the studies behind them, written to be understood without a biology degree. Two new pieces go up each week.

See all articles

Browse by topic

Ingredient Index

Every ingredient graded on what the trials actually show, in plain English, sorted by evidence rather than by hype.

Open the full index

More from Stratum

The rest of the publication — condition guides, the myths we've put on trial, everywhere we've been wrong and fixed it, and how to send us your own question.

Articles

Everything we've published, graded

Each piece carries the strength of its evidence at the top, so you know what you're reading before you read it. Pick a topic, or see the lot.

Or see every article in one list

The Sunday Study

One paper a week, taken apart properly

Three short pieces go up on the site each week. On Sunday we take a single study — usually a new one, occasionally an old one everybody has been misquoting — and give it the long treatment. That piece is the newsletter. It lands in your inbox and lives here afterwards. Every piece here is already graded on its own card below, so a second board just repeating those same grades back as a chart didn't earn its place on this page.

All topics

Evidence grade Jump to an article

Ingredient Index

Every ingredient, graded on what the trials show

Sorted by evidence, not by popularity. Where a claim rests on one small study, we say so.

Filter by concern Filter by evidence grade Jump to an ingredient

Also show formulation & minor-active ingredients

Conditions

Start from what's actually bothering you

The Ingredient Index and Articles are organised by molecule and by topic. These pages are organised by the question you actually arrived with — pulling together everything graded so far, in one place, ranked by how good the evidence is rather than how the page is titled.

Methodology

How to read a study, and how we grade one

Every grade on this site is a judgment call, made using the same handful of questions each time. This page is those questions, written out, so you can apply them yourself the next time a bottle promises something a study never quite said.

Claims on trial

The internet's favourite claims, graded fast

Whatever's trending on skincare Instagram or YouTube this month, in three or four paragraphs rather than a full article — one claim, one verdict, one grade. Have one for us to look at? Send it in.

Skin of colour

Where melanin-rich skin needs more than a footnote

Most dermatology trials, textbook photos and marketing claims default to lighter skin. That shows up in real ways for skin of colour — Black, South Asian, East Asian, Hispanic and Middle Eastern skin among others: conditions that look and present differently, a much higher post-inflammatory pigmentation and keloid risk, treatments that need retuning rather than just reusing, and whole topics (razor bumps, traction alopecia) that barely exist in mainstream skincare content at all. This page pulls together everything on the site that speaks to that directly, still graded on the same A–D scale as everywhere else — nothing here is graded more generously for appearing on this page.

Condition hubs

Full hubs where skin-of-colour presentation, risk or treatment nuance is significant enough to call out on the page itself.

Ingredients worth knowing about

Pulled from the hubs above — nothing here is a separate grade from the Ingredient Index.

Products checked against these ingredients

From the Products section — formulas that contain at least one ingredient listed above, checked the same way as every other product here: formula against claim, not the other way round.

India notes

Where the general evidence needs a local footnote

Most dermatology trials are run in temperate climates on Fitzpatrick I–III skin — the paler end of the six-type scale dermatologists use to classify how skin responds to sun, with VI the darkest. That doesn't make the findings wrong, but it does mean some of them need a footnote before they apply here. This is that footnote, collected in one place.

Corrections & grade changes

Everywhere we've been wrong, and what we did about it

We would rather be publicly wrong once than quietly wrong forever. Every time new evidence moves a grade, or we catch something we got wrong the first time, it's logged here with the date and what changed — nothing gets quietly edited out.

Ask Stratum

Send us a claim, a question, or an ingredient

If you've seen a claim you want graded, or you're stuck between two ingredients and can't tell which one the evidence actually supports, this is the queue. Reader questions are where most of "Claims on trial" and a good few full articles come from.

Products

Whole formulas, checked against the formula's own claims

The Ingredient Index grades single actives. This does the same job on finished products — reading the full INCI ingredient list a brand actually publishes, checking whether the ingredient behind the marketing claim is really there and roughly where the label's own framing implies, and saying plainly when we can't verify the formula at all.

How to read this section

We buy nothing on anyone's behalf and take nothing from any brand named here — this is the same non-negotiable as everything else on the site. INCI position is a real clue, not proof: cosmetic labelling rules only require descending order for ingredients above roughly 1% concentration; below that, order is often alphabetical. We say so per product rather than treating position as a verdict on its own. Every ingredient list below is sourced from the brand's own site and cross-checked against at least one independent source, and we tell you when sources disagreed instead of picking one silently. We link to each product's official page rather than reproducing the brand's own photography — the packaging icon here is ours, not theirs, and the link takes you to the real thing.

Filter by brand Filter by concern Filter by ingredient

About

We publish the evidence, including when it's weak

Skincare has an incentive problem. The people with the most reach usually have something to sell, and a claim propped up by one small company-funded study reads exactly like one backed by a decade of proper trials.

Stratum exists to keep those two apart. Every claim is graded, sourced and dated, and we rewrite pieces when the research moves. We also try to write like humans, because an explanation nobody finishes reading isn't much use to anyone.

Who writes this

The Stratum Editors. We are not doctors, dermatologists or cosmetic chemists. We are researchers who got tired of skincare claims that nobody could trace back to anything, and started reading the papers instead.

That limitation is the reason this site is built the way it is. We can’t ask you to trust our judgement, so we don’t: every claim carries its study, its grade, and a link straight to PubMed or the DOI so you can check our work without taking our word for any of it. Where we have got something wrong, we say so in the corrections log rather than quietly editing it.

Stratum runs a two-tier trust system, not one blanket claim of authority. Every published piece is evidence-graded — sourced, checked against the literature, and rated using the same methodology every time. A smaller, visibly rarer set of pieces will additionally be clinician-reviewed, meaning a named, qualified reviewer has checked it before publication. No article here has reached that second tier yet. Every article says so plainly at the top. When one does, the byline will name who reviewed it and what they are qualified in — and it will look different from the rest, on purpose.

Niacinamide rebuilds your barrier1, fades dark spots slowly2, and does almost nothing for wrinkles3.

What the Stratum Grade means

Latest articles

Ingredient Index

More from Stratum

Everything we've published, graded

One paper a week, taken apart properly

Every ingredient, graded on what the trials show

Start from what's actually bothering you

How to read a study, and how we grade one

The internet's favourite claims, graded fast

Where melanin-rich skin needs more than a footnote

Condition hubs

Ingredients worth knowing about

Related articles

Products checked against these ingredients

Where the general evidence needs a local footnote

Everywhere we've been wrong, and what we did about it

Send us a claim, a question, or an ingredient

Whole formulas, checked against the formula's own claims

We publish the evidence, including when it's weak

One paper a week, explained properly