Comedogenicity Ratings: How Reliable Are They, Really?

Where the ratings came from

The 0–5 comedogenic scale that floats around skincare blogs and apps comes from a series of studies done in the 1970s and 1980s. The methodology: apply test substances to the inside of rabbit ears, observe how many follicles plugged with sebum and keratin debris over a few weeks, score the substance from 0 (no plugging) to 5 (severe plugging).

The rabbit-ear model was a reasonable starting place when no better tool existed. It was never validated as a one-to-one predictor of human facial-skin behavior, and several known issues complicate the translation:

• Rabbit follicles are different from human follicles in size, density, and turnover rate.
• The test concentrations were often higher than typical cosmetic use.
• The test substance was often applied neat (pure), not in a finished formulation.
• Some substances rated comedogenic in the rabbit model do not produce comedones reliably on human faces; some rated non-comedogenic do produce them. ^[G20]

The 0–5 scale persists because it is simple, well-circulated, and approximately useful — but it is not a clinical gold standard. Treat the numbers as a starting prior, not a definitive answer ^[G3].

What the scale actually says

From the original ratings:

• 0 — Won't clog pores. Examples often listed: argan oil, hemp seed oil, sunflower oil (high-linoleic), squalane, mineral oil, beeswax (in small quantities).
• 1 — Low likelihood. Examples: castor oil, kukui oil, rosehip oil.
• 2 — Mild likelihood. Examples: olive oil, peach kernel oil, sweet almond oil.
• 3 — Moderate likelihood. Examples: avocado oil, soybean oil, isopropyl myristate.
• 4 — High likelihood. Examples: coconut oil, isopropyl palmitate, palm oil, cocoa butter (some sources).
• 5 — Very high likelihood. Examples: highly processed oleic-acid esters; less commonly seen ingredients.

Note that these placements vary across sources because different studies tested different forms of the same substance under different conditions. 'Comedogenicity rating of olive oil' is not a fixed number — it depends on the source.

What the ratings get right

A few patterns from the comedogenicity literature do hold up:

• Coconut oil and several esters (IPM, IPP) cause closed comedones in a meaningful fraction of acne-prone users on facial skin ^[G3]. Independent of the rabbit-ear study, dermatologists see this pattern in clinic.
• Linoleic-acid-rich oils (sunflower, hemp seed, prickly pear) tend to be friendlier to the barrier and to acne-prone skin than oleic-rich oils. ^{[G17] [G18]} This matches the 0–1 ratings for those oils.
• Mineral oil, despite its bad marketing reputation, has a strong non-comedogenic record. Petrolatum and dimethicone similarly tend to be 0 across sources.

These broad patterns reflect real fatty-acid-and-pore-biology mechanisms, not just rabbit ears.

What the ratings get wrong

A few ways the simple 0–5 scale leads people astray:

• It treats single ingredients as predictive of finished products. A formulation with a 'comedogenic' ingredient at 1% in a well-balanced moisturizer often does not break out the user; the finished formulation is what matters, not the single ingredient. ^[G19]
• It ignores context. Coconut oil at 100% on facial skin is meaningfully comedogenic; coconut oil at 2% in a body cream is not the same risk.
• It misses individual variation. Two people with similar skin types can have completely different reactions to the same ingredient. A '4' on the scale means 'high likelihood' across a population, not 'will definitely break you out.'
• It overstates the severity for some ingredients. Some 3s and 4s on the original scale are well-tolerated by most acne-prone users in finished products.
• It does not address fungal acne. The malassezia-feeding ingredient list is largely separate from the comedogenic ingredient list — there is some overlap (coconut oil is on both), but other ingredients are flagged on one and not the other ^[G5].

How to use ratings without overreacting

The practical way to apply comedogenicity ratings:

1. Use the rating as a starting prior, not a verdict. A '4' rating means 'higher chance of trouble for acne-prone users' — not 'definitely will not work.'
2. Weight position on the INCI (the ingredient list on the label). A '4' rating ingredient at position 25 on the INCI is in much smaller concentration than the same ingredient at position 3.
3. Account for your own reactions. If you have used an ingredient with a 'high' rating without issue for years, your own data outweighs the scale.
4. When troubleshooting a flare, ratings can help generate hypotheses. If you started a new product and broke out, the comedogenic rating of its ingredients is one input to consider when guessing what changed.
5. For severe acne, a derm visit is more useful than an ingredient list. No comedogenicity scale will substitute for evaluating the routine clinically.

What 'non-comedogenic' on a label means

Very little, formally. There is no standardized definition of the term, so in practice brands largely decide for themselves when to use it. 'Non-comedogenic' on a label typically means:

• The brand reviewed its ingredient list against some version of the comedogenicity scale and decided most of the ingredients are 0–2.
• The product was tested in a small in-house study with low-acne-history subjects.
• The brand is comfortable making the claim because it does not legally have to defend it.

Some 'non-comedogenic' products break out acne-prone users; some 'comedogenic' products do not. The label is a directional signal, not a guarantee.

The fungal-acne overlap

Separate from the standard comedogenic conversation, malassezia-feeding ingredients matter for fungal-acne-prone users ^[G5]. The malassezia list overlaps with the comedogenic list (coconut oil, oleic-rich oils) but extends to some ingredients that are not on the standard comedogenic scale:

• Many fatty-acid esters in the C11–C24 range.
• Polysorbates (sometimes flagged, evidence weaker).
• Olive oil, marula oil, camellia oil — comedogenic risk varies, but malassezia-feeding is more consistent.

If you suspect fungal acne (small itchy uniform bumps along the hairline or forehead that do not respond to salicylic acid, a common BHA exfoliant), the malassezia-safe list is a more useful filter than the comedogenicity scale. Fungal acne is a specific condition — Malassezia folliculitis — and it is usually managed with an antifungal ingredient (zinc pyrithione, ketoconazole, or sulfur) alongside oil avoidance, not by swapping oils alone ^[G5]. Because it is easy to mistake for ordinary acne, it is worth talking to a dermatologist — especially if it does not clear in about 4–6 weeks ^[G5].

What to actually do

• Treat comedogenicity ratings as a directional prior, not a verdict.
• If a product breaks you out, look at the high-rated ingredients near the top of the INCI.
• If a product agrees with you despite high-rated ingredients, trust your own results.
• For acne-prone users specifically, lean toward formulations with low-rated ingredients in the top 10 — but do not panic over a 3 at position 18.
• For fungal-acne-prone users, the malassezia-safe list is the more useful filter than the standard comedogenic scale — but fungal acne is a specific condition worth running by a dermatologist, since it usually needs an antifungal ingredient, not just an oil swap ^[G5].
• The 'non-comedogenic' label is unregulated — read the INCI, do not just trust the label.

Bottom line

The 0–5 comedogenicity scale is approximately useful and methodologically imperfect ^[G3]. Treat the numbers as a starting hypothesis rather than a final answer; weight your own skin's track record higher than any scale; and recognize that finished formulations matter more than single ingredients in isolation. Drop will flag high-comedogenic ingredients near the top of an INCI when your skin profile suggests it is worth flagging — and tell you when the scale is leading you to over-react to ingredients that, in context, are unlikely to cause problems.