3 Things You Need To Know About Comedogenicity Ratings

by Gio

why you can't trust comedogenicity ratings

Today I’m very excited to bring you a guest post by one of my favourite acne experts, Seppo Puusa. In his blog, Acne Einstein (what a great name is that?) he shares science-based advice on natural acne treatments. Here, he explains why comedogenicity ratings aren’t as reliable as you may think:

There’s danger lurking in every skincare bottle. Hidden deep beneath glossy marketing claims and polished labels lurk an untold number of comedogenic ingredients that threaten to turn your carefully cared face into acne battleground. Or at least if you listen to any of numerous comedogenicity experts out there.

As with many other things, commonly accepted ‘beauty blog wisdom’ doesn’t always line up with what science says. In this post we’ll go over 3 reasons you should take comedogenicity claims with a grain of salt.

Products with comedogenic ingredients aren’t automatically comedogenic

Many beauty bloggers like to post long lists of ingredients ranked by comedogenicity rating. Your duty is to check your skin care products against that list and discard any that contain comedogenic ingredients. This sort of detective work seems so.. scientific, and makes us feel smart.
It’s also utter rubbish.

In 2006 Dr. Draelos and colleagues showed that products with comedogenic ingredients don’t cause acne. Read that again. Products with comedogenic ingredient’s don’t cause acne.

In the study they tested 10 products with known comedogenic ingredients on 12 people prone to getting back acne. The products were applied on patches to the upper backs of the participants. The patches were changed every 48 to 72 hours, and this went on for 4 weeks. The researchers counted the number of comedones before and after the study and this was compared to both positive (highly comedogenic substance) and negative (nothing) controls.

These graphs show the results:


The graphs show relative increase in the number of comedones before/after the study. The authors note that any results +/- 10% of the negative controls are due to random variation and can be considered as non-comedogenic.

In short, none of the products containing comedogenic ingredients caused acne.

There are limitations to what we can conclude from this study. Most of the ingredients were rated between 1 and 3 in the comedogenicity scale, with only a few that were considered strongly comedogenic.

This apparent disconnect between comedogenicity ratings and real world results leads us to the next point.

Comedogenicity testing doesn’t reflect real life usage

Comedogenicity ratings are appealing because they seem to offer a simple answer to a complex problem. But you should keep in mind that this data hasn’t been generated by observing people using skincare products in everyday life. The data comes from ‘acne models’, both human and animal, and there are severe limitations to what we can conclude from the data.

Even if we set the ethics of animal testing aside, there are serious problems with animal models of acne. Mostly because no other animal experiences acne as commonly as humans do, and there are differences in human and animal skin that probably explains this.

Rabbit ear (REA), the most common acne model, is far more sensitive than human skin and produces scores of false positive results. A 2007 paper examining various acne models concluded that the rabbit ear model is only useful for determining absolute negatives.

Presently, the most commonly used assay is the REA, which possesses a hypersensitive response to acnegenic substances compared to human skin; however, this model is unable to accurately depict the acnegenic potential of chemical compounds, and is therefore only valuable for distinguishing absolute negatives. (Source: Mirshahpanah P. et al. Models in acnegenesis. Cutan Ocul Toxicol. 2007;26(3):195-202)

Human models, while better than animal models, are still far from perfect. Human models use highly exaggerated conditions to make the tests more sensitive. These include:

Subject selection. They usually only include people with large pores who are prone to getting pimples.

Application conditions. The test materials are applied under occlusion, meaning the area is covered after application. This increases absorption and skin penetration.

Dosage. The test materials are used in high concentrations. This doesn’t take dose response in account. A substance may cause acne at high concentrations but has no effect in concentrations found in skin care products.

2 cases where comedogenicity ratings are useful

This doesn’t mean that we should just throw away all the comedogenicity data. Rather, we should take it with a grain of salt. My view is that comedogenicity data is useful in two cases:

Determining absolute negatives. Since all the models are more sensitive than real life usage conditions, a substance with comedogenicity rating of 0 to 1 should be safe.

Determining worst offenders. Substances that rank high at the comedogenicity scale should be treated as potential suspects.

There’s so much uncertainty in the comedogenicity data that it’s not very useful for anything that falls between those two extremes.

Comedogenicity addiction can lead to bad purchasing decisions

Taking comedogenicity ratings too seriously unnecessarily limits your choices. You may end up paying more or choosing less than optimal products.
For example, comedogenicity is such a fear-inducing word that many people will pay more for products formulated without comedogenic ingredients – even if it’s a distinction without a difference.

And even if you don’t end up paying more, you may still pass on a good product because ‘it has comedogenic ingredients’.

Comedogenicity rule of thumb

I condensed everything that we’ve discussed earlier into a simple rule of thumb.

Be wary of products with strongly comedogenic ingredients high up on the ingredients list. Otherwise forget about it.

Some people may challenge me and say ‘the rule is dangerous because my skin always reacts to even mildly comedogenic ingredients’. That may be so, and I don’t doubt some people are like that. My point is that comedogenicity ratings are not reliable enough to make generalized recommendations. They may be helpful for someone, but then again, even a broken clock is correct twice a day.

And of course avoid any products/ingredients you know your skin reacts badly to – regardless of their comedogenicity rating.


To me comedogenicity ratings are a bit like astrology – just because someone made elaborate charts and systems doesn’t mean it’s correct. The scientific-looking ratings hide severe limitations.

The models used to generate the data are far more sensitive than real world skin care product usage, and they produce scored of false positive ratings. As such, the data isn’t very useful in guiding everyday skincare choices.

The best we can say is to avoid products with highly comedogenic ingredients high up on the ingredients list and ignore the rest.

Concerned about acne? Choosing noncomedogenic skin care products is a start, but for more reliable results, please check out my Comedogenicity Helpers email tips written specifically for Beautiful With Brains readers. Go here to get started ==> http://www.acneeinstein.com/comedogenicity-helpers/



Chic Readings October 7, 2014 - 5:46 pm

Thanks for sharing this, good to know:)

Gio October 7, 2014 - 6:01 pm

Helena, my pleasure. Glad you enjoyed it.

Allison October 9, 2014 - 6:35 pm

I agree with you, Gio. I had a friend respond to one of my fan page posts on FB that she needed to know whether a product I reviewed was noncomedogenic. I asked her why and she gave me a strange response. I told her that there was probably an ingredient that she reacts badly to and she needs to isolate that and avoid it. Not sure, I convinced her though

Gio October 9, 2014 - 6:57 pm

Allison, I hope you did. If she reacts badly to an ingredient, it’s best for her to avoid it. 🙂

anubhuti October 10, 2014 - 9:44 pm

very informative 🙂

Gio October 11, 2014 - 2:15 pm

Anubhuti, glad you found it useful. 🙂

Fact-check: How to Use Comedogenicity Ratings - Lab Muffin January 14, 2016 - 9:27 pm

[…] Beautiful With Brains – 3 Things You Need to Know About Comedogenicity Ratings […]

Comments are closed.