Methodology & Data Sources
Last updated: 2026-11-07
Where the ratings come from
Every 0-5 rating in the checker is traceable to published sources, and each one names its source. The primary source is the Fulton rabbit-ear assay (J. Soc. Cosmet. Chem., 1989), the largest controlled test of its kind: individual ingredients were applied inside rabbit ears and the resulting comedones and surface irritation were graded on a 0-5 scale. Where this database cites Fulton, the number is the assay's own.
The second source is the practitioner tradition: comedogenic ingredient lists maintained over decades by acne clinics and dermatologists, capturing ingredients the assay never tested and real-world observations the assay could not make. Where only the practitioner lists rate an ingredient, the entry says so - you will see the difference marked source by source in the results.
How we handle disagreement between sources
Published sources disagree, and pretending otherwise is how ingredient myths start. When the assay and the practitioner lists assign different numbers to the same ingredient, the checker shows a range - 3-4, 4-5 - instead of hiding the uncertainty behind one confident figure. A range is a feature: it tells you the honest state of the evidence.
Disagreement is sometimes the whole story. The database's most cited landmine is the lanolin family: Fulton's assay found acetylated lanolin itself non-comedogenic, while the offender, acetylated lanolin alcohol, rates 4/5 - and practitioner lists that lump the family together get both wrong. Refinement is a second recurring trap: coconut butter rated 4 in the assay while unrefined coconut oil carries 5 on clinical lists, and the difference between those two products is exactly the kind of detail a single-number list flattens away.
Beyond pore-clogging: irritancy and fungal-acne flags
Clogging is not the only way an ingredient can work against your skin. Where the same testing tradition measured surface irritation, the database carries a second 0-5 irritancy grade - an ingredient can be perfectly non-comedogenic and still sting. Both axes are shown because 'safe' and 'non-irritating' are different questions, and conflating them leads to the wrong substitutions.
The database also flags each ingredient's relationship with malassezia, the yeast behind fungal acne (malassezia folliculitis): trigger, safe, or caution, with the chemical mechanism - fatty-acid chain, ester, ferment, wax - recorded alongside the verdict. Acne-prone and fungal-prone routines fail for different reasons; a single-axis database cannot serve both, so this one carries both.
Known limitations, stated plainly
Rabbit ears are not human faces: the assay's follicles clog more readily than yours, which is why a 5/5 raw ingredient at 2% in a rinsed shampoo is not the same exposure as the same ingredient at 20% in a night cream. A rating describes the ingredient in isolation. Concentration, position in the ingredient list, the product's texture, whether it rinses off, and your skin's own tendencies all sit between the number and your face.
For that reason, this tool shows its data instead of issuing verdicts: every rating carries its source so you can weigh it. What the database is not is medical advice - persistent or cystic acne deserves a dermatologist, and ingredient data supports that conversation rather than replacing it. Use the checker to eliminate suspects, not to self-diagnose.