Comedogenic scale & comedogenic ingredients: Do they really cause acne?

Comedogenic ingredients are believed to cause clogged pores and blemishes. So checking the ingredient list of products for comedogenic ingredients in order to avoid acne is a great solution, right?

Well, not really. It's a little more complicated. An important point is that a single comedogenic ingredient may act differently than a mix of ingredients. Even if a product contains comedogenic ingredients, it doesn't necessarily mean that it will cause acne.

Let's dive deeper into the topic to be able to use the comedogenicity rating correctly.

What does 'comedogenic' mean? What is a comedogenic scale?

An ingredient is comedogenic if it is potentially pore-clogging.

The risk of an ingredient to clog pores is categorized as follows:

• ➣ 0 - non-comedogenic
• ➣ 1 - lightly comedogenic
• ➣ 2-3 - moderately comedogenic
• ➣ 4-5 - highly comedogenic

This categorization is also known as the comedogenic scale.

Btw, clogged pores are also called comedones (hence, comedogenic scale).

Where does the categorisation of comedogenic ingredients aka comedogenic scale come from?

In the 1970s, Albert Kligman and James Fulton (both dermatologists) tested ingredients for their comedogenicity. They basically invented the comedogenic scale.

For their tests, they used the so-called rabbit-ear-method. It's a common method to test the comedogenicity of ingredients.

The rabbit-ear-method involves applying ingredients to the insides of rabbits' ears and categorizing the ingredients depending on the formation of clogged pores (comedogenicity rating 0 to 5).

Are there downsides?

Yes, the rabbit-ear-model and the comedogenicity scale has 2 disadvantages:

1. The ears of rabbits are more sensitive than human skin
Did you ever touch the ears of a rabbit? So soft and fluffy! Much more delicate than human skin. And that's the point.

The development of clogged pores on the delicate ears is more likely than on human skin. This is why ingredients that do not cause problems on human skin have been classified as comedogenic.

A well-known example is the ingredient petroleum jelly/ vaseline. That's why there's still the myth that vaseline clogs the pores.

2. A single ingredient may act differently than a mix of ingredients
An ingredient may have a high comedogenic risk. However, if this ingredient is mixed with other ingredients, the risk may decrease.

And not only the mixing of ingredients is crucial. The dilution or concentration is also important. An example: The ingredient isopropyl isostearate has a comedogenicity rating of 4 at 100%, but only 1-2 at 5%.

How do we use the information about the comedogenicity of ingredients (comedogenic scale)?

It only makes sense to apply the comedogenic scale to the first 4 to 7 ingredients of a product since they make up the most of a product. The remaining ingredients have barely any effect on the skin (but there are exceptions).

The reason: The quantity makes the "poison".

A drop of a highly comedogenic ingredient (comedogenic scale: 5) in a product won't cause acne.

Keeping the above-mentioned in mind, you can use the comedogenicity scale to find strong positives and negatives:

If your skin is acne-prone, look for products that don't contain any comedogenic ingredients high up in the ingredient list. If a product consists of only one ingredient: avoid it if it's highly comedogenic or patch test the product. This is f.ex. the case with heavy face oils.

On the flip side: products that don't contain any comedogenic ingredients high up in the ingredient list are likely safe for your skin.

To sum up...

The importance of comedogenic ingredients in products is overrated.

Here's our recommendation:

If your skin is acne-prone: Be careful with products containing highly comedogenic ingredients (comedogenic scale 4 to 5) high up in the ingredient list (first 5 ingredients).

Hope this rule of thumb helps you! 

References and further reading:
Journal of the American Academy of Dermatology, 2006, 54, Pages 507-12. A re-evaluation of the comedogenicity concept.

Journal of the Society of Cosmetic Chemists, November /December 1989, 40, Pages 321-333. Comedogenicity and irritancy of commonly used ingredients in skin care products.

Journal of the Society of Cosmetic Chemists, August 1983, 34, Pages 215-225. Use of the rabbit ear model in evaluating the comedogenic potential of cosmetic ingredients.

JAMA Dermatology, 1 October 2018, 154(10), Pages 1131-1132. Myths, Truths, and Clinical Relevance of Comedogenicity Product Labeling.