Choosing the right skincare products can be a daunting task, especially when faced with a myriad of ingredients and formulations. One term that often comes up in discussions about skincare is "comedogenic rating". But what exactly does this rating mean, and how should you interpret it when selecting products for your skincare routine? In this blog post, we'll delve into the concept of comedogenic ratings, exploring their significance and providing insights into making informed choices for your skin.

Understanding Comedogenic Ratings

Comedogenicity refers to the likelihood of an ingredient or product to clog pores and cause acne. For people with acne-prone skin, this is extremely important to know for the following reason: Almost every anti-acne product dries out your skin (retinoids, benzyl peroxide, azelaic acid, etc.), so they need to find something that moisturizes the skin. As many moisturizers are comedogenic though, it can worsen the acne, which makes them use more drying anti-acne products, which requires a moisturizer to counteract the dryness, and so on - it's a vicious cycle. 

How can one break this cycle? By finding and using only products and moisturizers that are not comedogenic. The easiest way is to read product labels and choose only those that state “non-comedogenic” on them. However, not all companies do this and even if you do, how can you know if it’s really true? (There is no authority that controls the use of this term). The answer to this is the comedogenic rating. Ratings typically range from 0 to 5, with 0 being non-comedogenic (unlikely to cause pore blockages) and 5 being highly comedogenic (likely to cause pore blockages).

•     0 - Non-Comedogenic: Ingredients with a rating of 0 are considered safe for all types and are basically impossible to cause breakouts.
•     1 - Slightly Comedogenic: Products in this category are generally safe for many people but may cause issues for those with extremely acne-prone skin.
•     2 - Moderately Comedogenic: If used often, these ingredients may cause breakouts for those with oily and acne-prone skin. If you have light to moderate acne, you’re probably still fine
•     3 - Comedogenic: Ingredients with a rating of 3 have a higher likelihood of causing breakouts. If you have a history of acne, you should probably avoid it, even if you only have moderate acne. If you have very light acne, it is unlikely to worsen your condition.
•     4 - Highly Comedogenic: Ingredients in this category pose a significant risk of clogging pores and causing acne. Avoid them even if you have only light acne.
•     5 - Extremely Comedogenic: These are commonly the very best moisturizers because they occlude water but sadly this means that they generally occlude sebum and sweat as well and don’t let your skin breathe, which is a perfect nidus for acne bacteria. If you’ve never had a pimple in your life but suffer from extremely dry skin, these ingredients are going to do wonders for your skin.

How Is the Comedogenic Rating Assessed?

Contrary to what one might think, you cannot always evaluate the comedogenic rating of an ingredient on the mere basis of its chemical structure or properties. For example, sebum is primarily composed of triglycerides (= fats), fatty acids, wax esters and squalene. Plant oils are a mix of exactly these constituents. So in that case, all plant oils are comedogenic, right? Wrong. For example, jojoba oil is a plant oil that comes the closest to human sebum in terms of lipid constituents but nevertheless, it is given a rating of only 0-2/5. Why? One reason is that it has a very high oxidative stability. This means that it doesn’t get broken down by oxygen easily, which means that less free radicals are formed. Free radicals contribute to acne because they damage your skin barrier and cause inflammation. Another reason is that the molecules in jojoba oil are very small so they are more likely to penetrate your skin and therefore less likely to clog pores.

So now we know that it is not that easy to determine the comedogenicity just by looking at the chemical composition of the ingredient, there are just far too many additional factors playing in. So back to the original question: How is the comedogenic rating assessed, if not using the chemical structure?

It is evaluated using what’s called the “Rabbit Ear Test”: Each test substance gets applied once daily, five days a week for around three weeks to the external ear canal of New Zealand rabbits. The skin of the ears is then microscopically analyzed for the increase of follicular hyperkeratosis—an elevated production of keratin in hair follicles, which leads to clogged follicles and comedones over time. This is then compared to an untreated ear as a control and rated against its peer ingredients on a scale of 0-5 as follows:

0— No difference when compared to the control (untreated) ear section. 

1—Slight increase in keratin content within the follicle. 

2—Obvious increase in follicular hyperkeratosis

3—Marked increase of keratin and a hyperplasia (enlargement) of follicles.

4—Dilated follicles containing large amounts of impacted keratin.

5—Widely dilated follicles, filled with packed keratin causing partial or total blocking of sebaceous glands and ducts. Possible inflammatory changes.

  

Interpreting the Rating

Now you might ask yourself: “What? So it isn’t even tested in humans? How accurate will the comedogenic rating be then?” You’re absolutely right. There are a lot of problems with these studies:

1. The rabbit ear is far more sensitive than the human skin, so the ratings are widely exaggerated. A rating of 5 sounds horrible according to the rating table above but if you put it into this context, on human skin it might be rather a 3 or a 4.
2. The rating is qualitative, not quantitative. The numbered rating suggests a precise quantitative nature, which is sadly very far from the truth. If you check the table above, it is very subjectively assessed by what the human eye notices in change and then rated accordingly, which is obviously not exact at all. It would be better if you could actually measure the increase of keratin. This would give you hard numbers and make comparisons between substances more precise but unfortunately, this is very hard to measure.
3. Concentrations make a massive difference. The substances are always used at a concentration of 100%, which obviously does not reflect the cosmetic reality at all. An evaluation of vegetable oils by Kligman and Mills indicated that most had some degree of comedogenicity but the comedogenic rating became 0 when diluted to a 25% concentration in mineral oil. (Mineral oil is used because it has a comedogenic rating of 0, so it doesn’t skew the result).

 

So what can we conclude from these findings?

The comedogenic rating is a great approximation but you should definitely take it with a grain of salt. The good thing about it is, is that the ratings are very pessimistic, so if you trust them, you will always be on the safe side. A general rule of thumb is to make sure that ingredients with a comedogenic rating of 3-5 are not in the top 5 of the ingredient list. Then you can be assured that even if you’re prone to acne, the concentration of the comedogenic ingredients will be so much lower than tested in the studies that it most likely won’t worsen your condition.

In the quest for clear and healthy skin, understanding comedogenic ratings can be a valuable tool. However, it's important not to see these ratings as set in stone but as variables that have to be put into context of concentration in the product and sensitivity of your skin. The numbers represent a worst-case scenario, namely super-sensitive skin (Rabbit Ear Model) and a concentration of 100%. It lies in your responsibility to interpret these numbers appropriately.

 

Comedogenic Rating Table

 Below you can see a table with all major substances and their respective comedogenic rating. You can search for ingredients in the search bar and click on the headings to sort ingredients (alphabetically) and comedogenic rating (numerically) ascending or descending. If there's an ingredient missing, feel free to reach out to us and we'll check if there's any data on it!

Ingredient	Comedogenic Rating