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Ep 32: "Non-Comedogenic" is a Scam - Cosmetic Chemists Explain Why


We've all seen "non-comedogenic" on skincare packaging - it's the claim that promises the product won't clog your pores or cause breakouts. But the story behind "non-comedogenic" is quite messy, and the more you know about where this term came from, the less reassuring it gets.


Let's start with what acne actually is


Before we get into the non-comedogenic rabbit hole (literally), a quick rundown on acne types, in case you need a refresher


Most acne falls under the umbrella of acne vulgaris, and it generally starts the same way: a comedone. A comedone is a hair follicle that's been plugged by excess oil and dead skin cells. If it's open at the surface, it's a blackhead. If it's closed, it's a whitehead. And for the record, blackheads are dark because of melanin and lipid oxidation, not because your pores are dirty.


From there, things escalate depending on what happens to the comedone:


  1. Papules form when a comedone ruptures and releases bacteria into surrounding skin layers, causing inflammation. They're small and red with no pus.

  2. Pustules are papules that have become infected. This is the classic pimple: it has a red ring and a white center.

  3. Nodules form deeper in the skin when bacteria gets trapped further down. They're hard, painful, and often a precursor to cystic acne.

  4. Cystic acne is nodular acne but with a pus cavity. Usually the most severe, and most commonly seen in people with oily skin.


Dermatology tends to lump nodules and cysts together as "nodulocysts" since both sit deep under the skin and are inflammatory; the main difference is that cysts have a visible pus cavity and nodules don't.


Where "non-comedogenic" actually came from


It all started in 1972, with a study by Albert Kligman and Otto Mills. They introduced the concept of acne cosmetica: a specific type of low-grade, chronic acne that they believed was caused or worsened by topical cosmetic products.


Their observations were based on a group of women who had persistent mild acne that tended to appear in areas where cosmetics were commonly applied (mostly the chin, sometimes the cheeks, rarely the forehead). When those women stopped using cosmetics, the acne cleared up, often without any additional treatment. Some of these women had a history of teenage acne. Some had never had acne at all before using certain products. Either way, the pattern kept showing up.


The rabbit ear study


To figure out which products were causing the problem, Kligman and Mills developed a screening method: applying test materials to the ear canals of rabbits. There could be no issues with this, right?


Rabbit ears were chosen because they have large follicles, cycle quickly, and tend to form micro-comedones within one to two weeks, which makes them useful for rapid screening. They tested 25 popular moisturizing creams (selected, by their own admission, somewhat haphazardly from the shelves of Vanity Fair) and rated comedogenicity on a 0-3 scale, where 0 was none and 3 was roughly equivalent to human sebum.


Results:

  1. 11 products scored 0 (non-comedogenic)

  2. 6 scored 1

  3. 5 scored 2

  4. 3 scored 3


A few other things they noticed: adding 25% mineral oil to products completely removed their comedogenicity, which suggests that concentration and formulation matter more than any individual ingredient. They also found that modifying ingredients changed their comedogenicity significantly. One sample of petrolatum was very comedogenic, but a new sample from the same brand wasn't. Different grades of lanolin had different scores, and even different lanolin derivatives had different scores.


Hairsprays, cleansing lotions, and surfactant-based products were uniformly non-comedogenic.


Then they tested on humans


They applied the same products to the upper backs of two to three healthy adult male volunteers for six weeks, and not a single clear-cut breakout occurred. Now, it's important to note that this study was NOT well done - they applied it to "two to three" (is it two or three?) men, rather than a large sample size of women.


Early comedone formation was generally visible with the materials that had scored moderately in the rabbit model, but the highest grade any ingredient achieved on human skin was a 2. The authors themselves noted that rabbit ears are significantly more sensitive than human skin, and that human susceptibility varies enormously based on factors like whether someone has previously dealt with acne vulgaris.


They also couldn't prove that acne cosmetica was distinct from acne vulgaris because the two are completely indistinguishable under a microscope. They were working from observations and inferences, not hard evidence.


What came after


In the decade following, a few more studies chipped away at the original framework.

A follow-up study by the same researchers found that a human model could be used to evaluate comedogenicity, but that results didn't always match up to the rabbit ear model. Specifically, substances that rated a 1 in the animal model were non-comedogenic in humans.


In 1989, researcher James Fulton published the largest known list of ingredients tested on rabbit ears, which became the basis for most of the "comedogenic ingredient" databases that still circulate on the internet today.


Also in 1989, the American Academy of Dermatology determined that if a material didn't produce comedogenesis in the animal model, it was likely (not guaranteed) to be non-comedogenic in humans.


A 2006 re-evaluation found that some products weren't comedogenic even when they contained ingredients that had been found comedogenic at 100% concentration. It confirmed something the original study had already hinted at: concentration matters the most. The number of applications, the frequency, the duration, the method used to assess results, and the scoring system being used all affected outcomes.


So again, the conclusion is that the finished formulation is what matters, not the individual ingredients.


So what does "non-comedogenic" actually mean?


Legally? Nothing. There is no FDA standard or regulated definition for the term. Brands can put it on a label without meeting any specific testing requirement.


Scientifically? It's a little more complicated. The testing method that birthed the concept used rabbit ears, which are more sensitive than human skin. The human studies that followed showed that even moderately comedogenic ingredients didn't necessarily cause breakouts in real people. And the research consistently shows that whether something clogs your pores depends heavily on your individual skin, whether you've had acne before, the concentration of the ingredient in the finished product, and how the overall formula is constructed.


The original researchers said it well themselves: "Even the most comedogenic cosmetics will probably be harmless for most. The factor of individual susceptibility is paramount."


The actual takeaway


The non-comedogenic claim isn't useless, but it's not a guarantee either. If you're acne-prone, it's a reasonable starting point for filtering products. But the ingredient lists on Reddit and TikTok that flag individual ingredients as "pore-clogging"? Those are mostly based on rabbit ear data from 1972, tested at concentrations that don't reflect how those ingredients actually appear in finished products.


The science says the formulation is what matters, not individual ingredients.


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