Comedogenic ratings: where the 0–5 scale comes from and why it misleads

Premalatha

Ingredient Spotlight30 Oct 20265 min read

Comedogenic ratings: where the 0–5 scale comes from and why it misleads

Most comedogenic ratings online trace back to rabbit ear tests from the 1970s and 1980s. Why the 0–5 scale shifts with concentration, why an ingredient's number does not transfer to a finished product, and what brands should test instead.

By Dr. Premalatha, Ph.D., Life Science, Regulatory Consultant, Cosmetic Science Lab

Markets: globalEvidence: rabbit ear and human back studies, 1972–2007For: formulators and brand owners

Skin care Acne & oil control Formulation

Glass bottles of herb-infused plant oils with fresh rosemary and thyme on a wooden table

1972"acne cosmetica" first described [1]

4–5 → 1one ingredient's rating after dilution [6]

1 monthocclusion in the human back test [2]

Quick answer

What is the comedogenic scale? A 0–5 score for how strongly an ingredient produced comedones (clogged pores), mostly in the rabbit ear assay. 0 means none; 5 means severe.
Why it misleads: the rabbit ear is more sensitive than human skin [2], ratings change with concentration [6], and what matters is how the finished product behaves [5].
Oils are not one number. Coconut oil, cocoa butter, shea butter and argan oil differ in fatty acid profile, but use level and vehicle matter more than the oil's rating.
A non-comedogenic claim should rest on testing the finished product on human skin, not on an ingredient chart.

Take-home message for formulators

Screen ingredients with ratings if you must, then judge the whole formula
Record use levels, because the published number was usually measured at far higher strength

Take-home message for brand owners

Don't build a "non-comedogenic" claim from a checker tool
Ask for finished-product human testing, and expect customers to compare your INCI list with online ratings

01Why comedogenic ratings matter

Shoppers with acne-prone skin search for a comedogenic rating before they buy, and online checkers turn an INCI list into a colour-coded score. That makes the scale commercially powerful: one "4" next to coconut oil can sink a product. Yet the numbers were never designed to rank finished products.

Read with care

Comedogenic (forms comedones) is not the same as acnegenic (causes inflamed acne). Most ratings measure only the first.

02Where the 0–5 scale comes from

In 1972, Kligman and Mills described "acne cosmetica", mild acne linked to cosmetic use [1]. The workhorse test became the rabbit ear assay: ingredients were applied to the inner ear, and the follicles were graded for comedones. Fulton's group published rabbit-ear results for products and ingredients in 1984 [3], then tables of 0–5 scores for common skin care ingredients in 1989 [4]. Those tables still feed most online lists.

In 1982, Mills and Kligman added a human back model, applying substances under occlusion for a month. They found the rabbit more sensitive than human skin, and judged ingredients only weakly comedogenic in rabbits probably safe for most people, though acne-prone people may be an exception [2].

Timeline of the comedogenic scale from the 1972 description of acne cosmetica and rabbit ear assays to a 2007 review of acne models — **Figure 1.** How the comedogenic scale was built (orange), and the evidence that later limited it (green).

03The chemistry: fatty acids and oils

Plant oils and butters are mixtures of triglycerides, so their behaviour on skin follows their fatty acid profile. Researchers have hypothesised that sebum low in linoleic acid contributes to acne, and in a small one-month trial applying linoleic acid cut the overall size of microcomedones by almost 25% [8]. Oils rich in oleic acid or saturated stearic acid are not "bad", but they feel and behave differently.

**Table 1.** Common oils: dominant fatty acids and what their rating leaves out
Oil or butter	Dominant fatty acids	What a single rating misses
Coconut oil	Lauric, myristic (saturated)	Often rated high, yet works well at low levels or in rinse-off products
Cocoa butter	Stearic, palmitic, oleic	Rated 4 in the 1989 rabbit-ear tables [4], yet finished products using comedogenic ingredients are not necessarily comedogenic [6]
Shea butter	Stearic, oleic	Grade and use level change feel and occlusion; see body butter formulation
Avocado oil	Oleic	Rich, slow-absorbing; vehicle decides the outcome
Argan oil	Oleic, linoleic	Usually rated low; still occlusive at high use levels

04What the evidence says about the scale

Three findings explain why ratings do not transfer to finished products.

Concentration dependence. Rabbit-ear grades reported for acetylated lanolin alcohol are 4–5 at 50% but 1 at 2.5% [6]. Kligman noted that strongly comedogenic substances can become non-comedogenic after enough dilution [5].
Formulation context. You cannot tell from an ingredient list whether a product will be acnegenic [5]. Emulsifiers, other oils and the product type all change exposure.
Model limits. A 2007 review judged the rabbit ear useful mainly for identifying absolute negatives [7].

Bar chart: acetylated lanolin alcohol rated 4–5 at 50% in vehicle but 1 at 2.5% in vehicle — **Figure 2.** The same ingredient earns a different rating at a different concentration (rabbit-ear grades as reported by Draelos and DiNardo [6]).

05Formulation tips for acne-prone skin

Set use levels first.
A "4" oil at 1% in a gel-cream is a different exposure from the same oil at 30% in a balm.
Mind the vehicle.
A cleansing oil with a good emulsifier rinses away; a leave-on occlusive balm does not.
Balance the fatty acids.
Blend linoleic-rich oils for a lighter feel, and add antioxidants because they oxidise faster.
Test the finished product.
Support a non-comedogenic claim with a human comedogenicity study under dermatological supervision; see claims and clinical testing.

06For brands and formulators

If a competitor sells a "non-comedogenic" oil-based product, the INCI list shows the ingredients, not the use levels that make it work; deformulation and reading the INCI list recover that context. Our formulation team designs acne-friendly textures from the whole formula, not a ratings chart. Check single ingredients in our Ingredient A–Z, such as squalane or clays, and see our acne and oil control work.

07Questions readers ask

Is a comedogenic rating of 0 a guarantee?

No. It reflects a test result for the raw ingredient, usually in rabbits, not your skin or the finished product.

Is coconut oil comedogenic?

It is often rated high on online lists, but the effect depends on concentration and whether the product is rinse-off or leave-on.

What does "non-comedogenic" on a label mean?

It should mean the finished product was tested on people and did not increase comedones. Ask the brand what test supports it.

Need an acne-friendly formula that feels good?

We formulate, test and support non-comedogenic claims for skin care brands.

Explore formulation Talk to a formulator

08References

Kligman AM, Mills OH Jr. "Acne cosmetica". Arch Dermatol. 1972;106(6):843–850. PubMed
Mills OH Jr, Kligman AM. A human model for assessing comedogenic substances. Arch Dermatol. 1982;118(11):903–905. doi:10.1001/archderm.1982.01650230031022. JAMA Network
Fulton JE Jr, Pay SR, Fulton JE 3rd. Comedogenicity of current therapeutic products, cosmetics, and ingredients in the rabbit ear. J Am Acad Dermatol. 1984;10(1):96–105. doi:10.1016/s0190-9622(84)80050-x. PubMed
Fulton JE Jr. Comedogenicity and irritancy of commonly used ingredients in skin care products. J Soc Cosmet Chem. 1989;40(6):321–333. SCC library
Kligman AM. Petrolatum is not comedogenic in rabbits or humans: a critical reappraisal of the rabbit ear assay and the concept of "acne cosmetica". J Soc Cosmet Chem. 1996;47(1):41–48 (p. 46). SCC library
Draelos ZD, DiNardo JC. A re-evaluation of the comedogenicity concept. J Am Acad Dermatol. 2006;54(3):507–512. doi:10.1016/j.jaad.2005.11.1058. PubMed
Mirshahpanah P, Maibach HI. Models in acnegenesis. Cutan Ocul Toxicol. 2007;26(3):195–202. doi:10.1080/15569520701502815. PubMed
Letawe C, Boone M, Piérard GE. Digital image analysis of the effect of topically applied linoleic acid on acne microcomedones. Clin Exp Dermatol. 1998;23(2):56–58. doi:10.1046/j.1365-2230.1998.00315.x. PubMed

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Dr. PremalathaPh.D., Life Science, Regulatory Consultant, Cosmetic Science Lab · Last reviewed 30 Oct 2026Product formulation

Update log

30 Oct 2026Published by Cosmetic Science Lab

This article is general technical information, not legal, regulatory or medical advice. Confirm requirements for your product and market before launch.