How we grade the evidence (and why "clinically studied" isn't "proven")
Every product page on this site links back to this library, and every claim in this library is graded. This page explains the grading, so you can hold us to it.
The tiers we use
Tier 1 — clinical-setting evidence. Studies run under medical supervision: injections, post-procedure protocols, wound care. This is where PDRN's strongest research lives. It is also the tier most often borrowed by cosmetics marketing — an injectable study says nothing direct about a serum. When evidence is Tier 1, we say so, and we say what it does not cover.
Tier 2 — topical human studies. Creams and serums tested on human skin, ideally randomised and vehicle-controlled. This is the tier a cosmetic claim actually needs. Much of K-beauty's most interesting research sits here, but studies are often small (tens of participants) and short (weeks, not years). Small and short does not mean wrong — it means the honest claim is narrower than the advertising.
Tier 3 — mechanism and lab evidence. Cell cultures, reconstructed skin models, biochemical pathways. Mechanisms are genuinely useful — they explain how something could work — but a pathway in a dish is a hypothesis about your face, not a result on it.
Tier 4 — tradition and anecdote. "Used for centuries", influencer results, before-and-after photos. We treat this tier as a reason to run better studies, never as a reason to make a claim.
What "clinically studied" means on this site
It means a study exists and we can point at it — nothing more. It does not mean the study was on the finished product you are holding, at the same concentration, on skin like yours. Where those gaps exist, the product page says so.
The two questions we ask of any study
- Was it on humans, on intact skin, with the ingredient applied topically? If not, the result belongs to a different tier than the marketing usually implies.
- Compared to what? Skin improves with moisturisation alone. A result only counts when the formulation beat its own base — the same product minus the hero ingredient.
Why we bother
"Dermatologist-approved", "clinically proven", "visible results in 7 days" — beauty marketing language has trained everyone to skim past claims. We think the opposite approach is a better trade: tell you exactly how strong the evidence is, including when it is thin, and let the products earn trust at their real size. An informed member who buys one right product is worth more to us — and to their skin — than a converted stranger who buys three wrong ones.
This article describes how we assess cosmetic-ingredient research. It is general information, not medical advice.
