Comedogenic ingredient lists: why the online rankings mislead

Search “comedogenic ingredients” and you’ll find dozens of charts rating oils, waxes and emollients from 0 to 5, plus apps that scan a label and flag anything above a 2. They look precise. They’re built on a foundation most sites copying them have never read: a handful of rabbit-ear experiments from the 1980s. Here’s where the numbers came from, and why coconut oil is the perfect example of a rating that’s both true and misleading.

Where the 0-to-5 numbers came from

In the 1970s and 80s, dermatologists were trying to explain acne cosmetica, the small persistent breakouts some adults got from their cosmetics. To find the culprits, they turned to the inside of the rabbit ear, whose large follicles plug visibly when exposed to certain substances. A follicle is the tiny tube in skin that a hair grows from and that sebum, the skin’s oil, flows through; a plugged one is a comedone, the blackhead or whitehead acne starts from.

The most-copied table comes from a 1989 survey in a cosmetic chemistry journal. Its method: dilute the ingredient, typically to 10 percent in propylene glycol, apply 1 mL to the inner ear daily, five days a week, for two weeks, then measure the width of the follicular plugs by eye and under a microscope. Grades 0 to 1 were considered minimal, 2 to 3 borderline, and 4 to 5 reproducibly positive. Isopropyl myristate, a common emollient, served as the positive control: the known plugger every run was compared against.

That table is where the familiar numbers originate. Isopropyl myristate and laureth-4 score 5. Lauric acid, cocoa butter and coconut oil score 4. Acetylated lanolin alcohol scores 4, while plain anhydrous lanolin scores 0 to 1. Mineral oil, glycerin and propylene glycol score 0. Olive oil scores 2.

Notice the details the online charts usually leave out: rabbit skin, one ingredient at a time, a set concentration, a specific schedule, and the author’s own note that results “depend on source of raw material”. The same oil from two suppliers could score differently.

What the rabbit ear actually measured

The rabbit ear was chosen because it’s sensitive, and that turned out to be its biggest flaw. In 1982, the dermatologists behind much of the original rabbit work published a human version of the test and stated plainly: the rabbit model is more sensitive than the human. Substances only weakly comedogenic in rabbits were, in their words, probably safe for human use, with the possible exception of acne-prone people.

So a rabbit score exaggerates. A 2 or 3 in the rabbit may be nothing on a person. Even a 4 or 5 means an ingredient can plug follicles under strong exposure, not that it will plug yours at lotion levels.

The 1989 author also drew general rules from his data, and they explain the pattern better than any single rating:

• Medium-chain fatty acids (lauric and myristic acid and their relatives) plug follicles more than shorter or longer chains do.
• Attaching a molecule to a sugar or increasing its ethoxylation (adding ethylene oxide chains, which makes it more water-loving) tends to reduce plugging.
• Very long-chain lipids, the waxes, appear too large to cause a reaction at all.

Those rules are chemistry, not a list of ingredients to fear.

Why the numbers don’t transfer to your face

Two things change between a rabbit ear and a product on your skin: concentration and company.

Concentration

An ingredient tested at 10 percent, applied daily and left in place, is a different exposure from the same ingredient making up 1 or 2 percent of a moisturizer you spread thinly. Comedone formation takes weeks, which is why the tests run for a month under occlusion, and depends on how much of a substance reaches the follicle and stays there. Ingredient lists run from largest amount to smallest, so a “4” near the bottom of a label is a different matter from a “4” in second place.

Company

The rest of the formula matters at least as much. Emulsifiers, water, humectants and how fast a product absorbs all change how much of any ingredient reaches a follicle. In 2006, two dermatologists patch-tested finished cosmetics containing supposedly comedogenic ingredients on six comedone-prone volunteers for four weeks. Their conclusion: finished products using comedogenic ingredients are not necessarily comedogenic. A 2021 human trial found the same from the other side: creams containing lanolin and several plant oils, ingredients on many “avoid” lists, passed a four-week comedogenicity test.

A chart can’t capture any of this; it only knows the ingredient’s name.

Coconut oil: the classic example

No ingredient illustrates the problem better than coconut oil. It scores 4 in the 1989 table, a rating repeated on nearly every online list, usually with a warning to avoid anything containing it.

The rating is real. Coconut oil is roughly 45 to 55 percent lauric acid, a medium-chain fatty acid that scores 4 on its own, and a small 2025 case-control study of 151 women linked facial cleansers containing comedogenic ingredients, mostly lauric and stearic acid, to about two and a half times the odds of acne. So if you rub pure coconut oil into an acne-prone face every night, the chart’s warning is fair.

But the same lauric acid is, in laboratory studies, strongly antibacterial against the bacterium involved in acne, which is why researchers have looked at it as a possible acne ingredient. And a lotion dilutes it, a wash rinses it off, and many “coconut-derived” ingredients are processed derivatives rather than the oil itself. “Contains coconut” can mean a heavy pure oil, a trace in a formula, or a derivative that shares little more than a name.

The honest answer to “is coconut oil comedogenic?”: pure, on an acne-prone face, likely yes; in a product, it depends on the product, and only a test of that product can say.

What the lists get right

None of this makes the tables worthless. They were careful work for their time, and they captured real chemistry: medium-chain fatty acids and certain esters do plug follicles more readily than waxes or simple humectants. If you’re choosing between two pure oils to apply on their own, the ratings are a reasonable guide. A high-scoring ingredient in the first few positions of a leave-on product is a fair reason for caution.

The problem isn’t the data. It’s the way it’s been stripped of context: the rabbit, the concentration, the single-ingredient design and the author’s own caveats.

How to read an ingredient list without being misled

• Rank beats rating. Ingredients near the top of the label make up most of the product; those at the bottom are present in small amounts.
• Leave-on beats rinse-off. Save most of your scrutiny for moisturizers, sunscreens, foundations and hair products that stay on your skin all day.
• Whole-product testing beats charts. A maker that describes a human test on the finished product is giving you better information than any app can.
• Your skin beats everything. Introduce one product at a time, give it several weeks, and drop it if small bumps appear.

If breakouts persist no matter how carefully you choose, or you have deep or painful spots, see your doctor or pharmacist. Ingredient avoidance has limits; treatment goes further.

The comedogenic scale came from single ingredients painted into rabbit ears in the 1980s, a model known even then to be more sensitive than human skin. Concentration and formula decide what a product does, which is why products with “comedogenic” ingredients often pass human tests and why coconut oil’s 4 is true in a jar and unhelpful on a label. Use the lists as hints, and let human testing and your own skin have the last word.