Things You Need to Know About Comedogenicity Ratings

Curated by Claudia Shannon / Research Scientist / ishonest

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 ingredients don’t cause acne.

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.

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.

Conclusion

Seppo Puusa is the founder of Acne Einstein (what a great name is that?), an acne blog where he shares science-based advice on natural acne treatments. He’s a science nerd who is also passionate about health and loves digging through medical journals for acne treatment gems he can share with fellow acne sufferers.

Read more on: comedo


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