Almost every conversation about pore-clogging skincare eventually points to a single number between 0 and 5. It looks authoritative, and it is genuinely useful — but only if you understand where it came from and what it can and cannot tell you. This is the full story of the comedogenic scale: its origins, its meaning, and its real limits.
What the numbers mean
The scale rates an ingredient's tendency to form comedones — the plugs of oil and dead skin that become blackheads and whiteheads. A 0 means an ingredient will not clog pores for virtually anyone. A 1 or 2 is low-risk and falls within what most people mean by “non-comedogenic.” A 3 is the moderate midpoint. A 4 or 5 is high-risk, with a real likelihood of clogging pores on acne-prone skin. In practice, dermatology writers treat 0–2 as the safe zone and reserve caution for 3 and above.
Where the scale came from
The ratings most sites use — including this one — descend from research by dermatologist James Fulton, better known as a co-developer of tretinoin (Retin-A). In the 1970s and 1980s Fulton and colleagues applied cosmetic ingredients to the inside of rabbit ears, a site whose follicles react strongly and predictably, then graded the follicular plugging on a 0–5 scale. That rabbit-ear assay produced the first large, systematic ranking of comedogenic ingredients, and it is why isopropyl myristate, certain lanolin derivatives, and cocoa butter have carried high scores for decades.
Fulton himself later cautioned against reading the numbers too literally, noting that a finished cosmetic's formulation could change an ingredient's behaviour. That nuance is often lost when a raw 0–5 list gets copied across the internet.
Why the scale is imperfect
Three limitations matter most. First, species and site: rabbit ear skin is more sensitive than human facial skin, so the test can flag ingredients that cause few problems on people. Second, concentration: ingredients were tested at high, often undiluted, levels — far above what a real product contains. Acetylated lanolin alcohol, for example, can rate 4–5 at full strength but behaves far more mildly at the small percentages used in actual formulas. Third, formulation: the other ingredients around it, the delivery system, and the overall chemistry can raise or lower how comedogenic a given ingredient actually is on your face.
There is also a practical point the raw number can't express: order on the label. Ingredient lists run in descending order of concentration, so a 4-rated ingredient in the final third of a long list is usually present in trace amounts and unlikely to matter. A 3 in the first few ingredients is a bigger deal than a 5 at the very end.
How to actually use it
Treat the comedogenic scale as a screening tool, not a verdict. Use it to shortlist products worth a closer look and to make sense of a breakout you can't explain — if a new foundation is high on the scale and your skin reacted, that is a useful clue. But don't discard a product you love over a single mid-range number, and don't assume a low average guarantees clear skin. The most reliable test is still your own: patch, observe, and let the ratings inform rather than dictate.
Ready to put a product through it? Run its ingredients through the comedogenic checker, or browse the full ratings table.
Frequently asked questions
Who invented the comedogenic scale?
The scale is rooted in work by dermatologist James Fulton, co-inventor of tretinoin, who in the 1980s tested ingredients on rabbit ears and scored how strongly they formed follicular plugs. Most 0–5 lists circulating today derive from that research.
Is a rabbit-ear test relevant to human skin?
Partly. The rabbit-ear assay is sensitive and reproducible, which made it useful for ranking ingredients, but rabbit ear follicles are more reactive than human facial skin, so the test can overstate risk. It's a directional guide, not a precise prediction.
Should I avoid everything rated 3 or above?
No. A rating tells you an ingredient's potential, not its guaranteed effect. Concentration, where it sits on the label, the finished formula, and your own skin all matter. Many people use products with a 3 or 4 ingredient without any problem.
Sources
- Fulton JE et al. — Comedogenicity of current therapeutic products, cosmetics, and ingredients in the rabbit ear (J Am Acad Dermatol, 1984) and Fulton's 1989 comedogenicity ratings
- Platinum Skin Care — Comedogenic Ratings (comedogenic + irritancy table)
- SkinScore — Comedogenic Ingredients: Complete List With Ratings
- Kristina Markovic — Comedogenic Rating: Oils, Butters and Cosmetic Ingredients
- INCIDecoder — On Comedogenic and Irritancy Ratings
- Lab Muffin Beauty Science — How to Use Comedogenicity Ratings
Informational only, not medical advice.