How we rate ingredients
This page exists because most sites publishing pore-clogging lists never explain where their numbers came from. Ours should be checkable.
Where the ratings come from
Comedogenicity ratings originate in work by Albert Kligman and O.H. Mills in the 1970s, which assessed follicular occlusion using the rabbit ear canal, later refined with human follicular biopsy studies. Essentially every “pore-clogging ingredients” list in circulation descends from that literature, usually several copies removed.
We record a rating only where we can trace it to that body of work or to a consistent reading across independent sources. Where we cannot, we still list the ingredient — but we mark the rating disputed rather than quietly picking a number.
Evidence grades
Every ingredient carries one of three grades:
Traceable to published comedogenicity testing, consistent across sources.
Reasonably supported, but from fewer or less direct sources.
Sources disagree, or the figure circulates without a clear original citation.
What these ratings cannot tell you
A comedogenicity rating describes a raw ingredient tested in isolation, usually at a concentration far above what appears in a finished product. It says nothing about:
- How much of the ingredient is in the product you are holding
- Where it sits in the INCI list, which tracks concentration
- Whether the product is rinse-off or leave-on
- How the rest of the formula changes its behaviour on skin
- How your skin responds, which is the only test that ultimately counts
This is why we present the checker as triage. Several high-rated ingredients near the top of a list is a real signal. One 3-rated ingredient at the very end usually is not.
What we will not do
- Call an ingredient “toxic” or a “chemical” as a scare word. Everything is a chemical.
- Imply that natural means safe, or that synthetic means harmful. Neither holds.
- Publish a health claim we cannot point at a source for.
- Present a disputed number as settled because a cleaner answer converts better.
Corrections
If a rating here is wrong, or a source contradicts it, we want to know. Send the ingredient and the source and we will update the entry or move it to disputed.