How SeoulHabit Grades Ingredients

Published: July 25, 2026 · Last updated: July 25, 2026

SeoulHabit is a Korean skincare store that publishes evidence grades for skincare ingredients. This page explains how every grade is assigned, so you can check our work.

The disclosure, first

SeoulHabit sells products that contain some of the ingredients graded on this site — that is a financial relationship, and you should know about it before you read any grade. The grades are written by Kim, SeoulHabit's founder. Kim is not a dermatologist or a chemist; he is a retailer who reads the studies and shows you the sources. The same disclosure appears on every video and every ingredient page — not just here.

The four tiers

Every ingredient we cover receives exactly one grade:

Tier 1 — Clinical evidence. Studies on real people, published in peer-reviewed journals, measured a change in how skin looks or feels.

Tier 2 — Lab evidence. Effects measured in cells or laboratory models. Lab results do not automatically translate to results on skin, and we say so wherever we cite them.

Tier 3 — Traditional use. A long, documented history of use, with little or no formal study. Tradition is information, not proof, and we grade it as what it is.

Tier 4 — Marketing claims. Claims we could only find in brand materials, with no independent evidence located. We never base a recommendation on Tier 4 evidence.

Mixed. The evidence genuinely points in different directions. When that happens, we show both sides rather than picking the flattering one.

What counts as evidence — and what doesn't

Evidence that counts: peer-reviewed studies, publicly available and named on the page; the ingredient list printed on the product (the INCI list), which we treat as the source of truth — if the INCI list is silent on something, we do not claim it.

Evidence that does not count: brand marketing materials, popularity, follower counts, how well a product sells, and what SeoulHabit happens to stock.

Every statistic and quotation on an ingredient page names its source, inline, with a link and a date.

The rules we grade by

The evidence sets the grade. What SeoulHabit stocks is not an input to grading, at any tier.
Stocked status is disclosed wherever a grade appears — identically in both directions, including where an ingredient we sell grades low.
The rubric is applied identically to ingredients we stock and ingredients we don't, and that neutrality is documented publicly, here.
Grades revise only on new evidence. Every revision is dated and states what evidence changed. A grade is never revised because of a commercial outcome.
Every grade must be defensible to someone who sells this ingredient and to someone who doesn't. A grade that only survives one of those audiences is a position, not a grade.
At least one of the first eight ingredients we cover carries a low or mixed grade, visibly, on camera.

When grades change

New evidence changes grades — that is the system working. Every revision is listed on the ingredient's page with the date and the evidence that prompted it. Sales performance, inventory, and partnerships are never reasons to revise a grade.

Challenge a grade

If you believe a grade is wrong, tell us through the contact form on our site. Include the source you think we missed or misread. We review every challenge against the rubric above, and if the evidence warrants it, the grade changes — dated, with the change explained on the page.