The SkinSort Blog

Comedogenic + Irritancy Ratings - What you need to know

Updated: December 21, 2023

SkinSort displays comedogenic and irritancy ratings for certain ingredients. This post is here to explain what those ratings mean, and how you should interpret them.


Comedones are a form of acne caused by clogged pores. Comedogenic ratings were designed to measure the likelihood of an ingredient to cause comedones.

On the other hand, irritancy ratings indicate the likelyhood of an ingredient to cause skin irritation.

Many people use these ratings to avoid acne-causing ingredients. Should you?

It's complicated. There's a lot debate out there on the whether or not these ratings should be trusted.

The quick answer:

  • Comedogenic and irritancy ratings don't usually tell the whole story.
  • They can be a useful source of information about an ingredient - and it's reasonable to take them into consideration when evaluating a formulation

In this post, we'll take a closer look at the history, science, and truth behind these numbers.

What is a comedogenic rating?

The term "comedogenic" is used to describe any ingredient that may cause comedones.

Like we mentioned earlier, comedones are the scientific name for acne caused by clogged-pores.

A comedogenic ingredient means it is more likely to cause clogged pores. When pores are clogged, the bacteria trapped inside inflames your skin and causes acne.

The comedogenic rating system is numbered 0 - 5.

A 0 on the scale means an ingredient has no chance of clogging pores.

On the flipside, an ingredient with a rating of 5 is very likely to clog pores.

There are tons of resources on the internet that can help you decipher which ingredients are comedogenic and which are not (including our ingredient checker!).

However, there's a lot more to these charts, graphs, and lists than just the numbers.

History

The initial concept of a comedogenic test was first developed in the 1970's.

In 1972, Dr. Albert Kligman and Dr. James Fulton conducted comedogenic studies on rabbit ears.

These two dermatologists also invented the term "acne cosmetica", or acne caused by using cosmetic products.

During the studies, ingredients were applied to the rabbits' ears and analyzed a couple of weeks later.

Researchers looked for comedones and rough patches of skin using microscope samples and visual methods.

Why rabbit ears?

Rabbit ears were used in this study due to their sensitivity and affordability.

Because the rabbits' ears reacted more quickly, the researchers were able to gather comedogenic rating results faster.

The Scale

From these studies the 0 - 5 scale was developed.

Here's how these numbers are classified:

  • 4 - 5 is the presence of large comedones and significant increase in rough skin patches
  • 2 - 3 indicates a modest amount of large comedones or significant increase in rough skin patches
  • 0 - 1 had little to no significant increase in comedones or rough patches

Comedogenic ingredients were divided into 12 groups:

  1. Lanolins
  2. Fatty Acids
  3. Alcohols / Sugars
  4. Waxes
  5. Thickeners
  6. Oils
  7. Pigments
  8. Silicones
  9. Sterols
  10. Vitamins / Herbs
  11. Preservatives
  12. Miscellaneous

The study concluded with advice for those with oily or acne-prone skin to avoid using high comedogenic ingredients.

Since then, additional studies have been done using humans as test subjects with similar results.

A 1982 study found the following:

(ingredients) that are moderately to strongly comedogenic in the rabbit ear model test have been found to be capable of inducing comedones in the human model described in this report....(ingredients) that are weakly comedogenic in the rabbit are probably safe for human use with the possible exception of acne-prone persons

So, what's the catch?

While those studies sound promising, there are some caveats that everyone should know.

The truth is, comedogenic ratings shouldn't always be taken for face value.

Here's why:

1) Rabbit Ears are not a good indicator

The 1972 study using rabbit ears cannot be translated to human skin.

Rabbit ears are more sensitive than human skin. They also have naturally large pores.

In the years following the study, there was controversy over false-positive results.

Many experts state that the results were skewed, since rabbit ears are much more sensitive than our skin.

They stated that the naturally large pores of rabbit ears also led to incorrect analysis of the results.

Have you heard of petroleum jelly, or vaseline, causing pimples? That myth arose from this study.

Turns out, petroleum jelly is non-comedogenic and has since been given a rating of 0.

Since then, other ingredients have been reconsidered by Dr. James Fulton himself.

Dr. Howard Maibach, Dermatologist and professor at UC San Francisco completely dismisses the rabbit ear tests.

In a published article, he states rabbit ear tests are "only valuable for distinguishing absolute negatives".

2) Limited Human Testing

The 1982 study using human test subjects found similar results to the rabbit ear test.

However, they did state that weakly comedogenic ingredients for rabbit ears are most likely safe for human use.

The problem with this study? The testing was done on the backs of young males with large pores.

As we know, back skin and face skin are different. Not only is body skin more hardy, it also contains less pores than our face.

Another study from 2021 on males looked at comedogenicity of ethylhexyl palmitate (AKA octyl palmitate in the study).

The participants were given a pad with the ingredient and adhered to the skin by tape.

The study found ethylhexyl palmitate increased comedones on every participant by at least 50%. The sample size, or number of participants, was just 15 adults.

I'll hazard a guess that most of us aren't applying a pad and tape over our skincare every day.

Tape is an occlusive in itself and may be the result of acne. Many studies done on humans involve an occlusive patch.

The study itself includes this disclaimer:

It is important to emphasize that our study design under occlusive condition for 4 weeks is not indicative of the normal use of products under non-occlusion for several weeks or months.

3) Individual Ingredients vs. Entire Formulation

Comedogenic ratings are accounted for an ingredient, but not the entire product.

Why does this matter? Our skincare products are made up of many ingredients that all play a role.

The comedogenic ratings of an ingredient is affected by the other ingredients.

A 1996 study highly-comedogenic (4-5) ingredients became non-comedogenic (0-1) after sufficient dilution. On the flip side, combining ingredients can increase comedogenicity.

Another thing to look out for is the source of products.

Oils and extracts from plants may vary in comedogenic rating. Some sources may be more comedogenic than others due to origin.

Unfortunately, it is impossible to know where an ingredient originates from without contacting the supplier.

Dr. Michelle Wong of Lab Muffin Beauty Science states it eloquently:

even if an ingredient is comedogenic on its own, it might not be comedogenic in a product. And even if a product contains no comedogenic ingredients, it can still be comedogenic on the skin.

Quantity Matters

The amount of an ingredient in a formulation also impacts it's likelihood to cause comedones.

Ingredients that are further down on an ingredient list are present in lower percentages than those higher on the list.

For example - an ingredient with a comedogenic rating of 3 that appears at the bottom of a formulation is far less likely to cause comedones when compared with a formulation that has that ingredient at the top.

4) Uniqueness of your skin

Dermatologists and skin experts all agree the chemistry of your skin plays a role in comodone creation.

While an ingredient may clog pores for others may not be true for your skin.

5) Lack of research

The previous four points bring us to the fifth: *there is simply not enough research on real-world conditions to say comedogenic ratings are definitive. *

In order to understand if a product will clog pores, more studies are needed.

1) Testing done with more realistic conditions
2) Testing should be done using products and not single ingredients

At this time it's hard to say with certainty if an ingredient in a product will cause clogged pores.

Until science reveals more, comedogenic ratings should be used as a suggestion and not as final say.

In an article recalling the original comedogenic rating given to petroleum jelly, Dr. Albert Kligman states:

One cannot determine from a reading of the ingredients whether a given product will be acnegenic or not. What matters solely is the behaviour of the product itself

Comedogenic Ratings on SkinSort

We display comedogenic and irritancy ratings on SkinSort, and acknowledge that they're an imperfect metric.

Our goal is to provide you with all of the information that you need to make informed decisions about the cosmetic products you purchase.

As these ratings are controversial, we've made sure to include a link to this post wherever we display these ratings on our site.

Feel free to consider these ratings when researching a product, but we recommend doing further research.

Comedogenic Ratings Are Not Personal

Comedogenic ratings aren't tied to your skin - this is why we built out a way for you to like + dislike ingredients on SkinSort.

If there are ingredients that you like or dislike, you can set them with your SkinSort account.

We'll let you know when a product contains them. This is a more reliable way to avoid ingredients your skin doesn't like, as it's based on your own experience.

Our "Non-Comedogenic" Filter

We've added a "Non-Comedogenic" filter to our product database.

As the term is unregulated, we defined it as the following with our filter:

Does not contain any ingredient with a comedogenic rating of 2 or higher

The filter is provided as a starting point for product discovery, but by no means is it a guarantee that a product won't/will cause comedones.

Recommendations

While we eagerly await new research relating to comedogenic ratings, here are some tips to follow in order to prevent clogged pores.

Comedogenic Charts

As we mentioned before, comedogenic charts should be treated as a suggestion and not an absolute guideline.

Those with oily, acne-prone, or sensitive skin should avoid highly comedogenic ingredients.

Remember ingredients that clog pores for others may not necessarily react with your skin chemistry. Discrepancies in comedogenic charts is due to the lack of standardization.

You can also find comedogenic rating tables in scholarly articles, such as the ones from the rabbit ear tests.

Irritancy Ratings

Irritancy ratings come from the same studies as the comedogenic ratings, and thus should only be used as a general guideline.

Patch test

It is best to patch-test new products. The American Academy of Dermatology recommends these steps for patch-testing:

1) Apply to the same spot, twice a day, for 7-10 days
2) Keep the product on for as long as you normally would
3) Be mindful of ingredients with temporary irritation, such as retinol.
4) If you are having an adverse skin reaction, be sure to wash and treat the area gently.

Be careful of labels

When out shopping for a new product, be mindful of packaging that claims a product does not clog pores.

The term comedogenic is not regulated and unstandardized.

This means no one is double-checking to make sure a product is truly non-comedogenic and will not clog pores.

Be sure to check the product's ingredient list to get a better feel on how pore clogging it might actually be.

You can run the ingredients through our ingredient checker to get an idea of if the product contains any potentially comedogenic ingredients.

Wrap-up

While the research behind comedogenic ratings is flawed, it can still be worth referencing these ratings.

They should be used as suggestions rather than hard guidelines.

Dermatologists recommend those with oily, sensitive, or acne-prone skin to be careful about highly comedogenic ingredients.

Remember your skin chemistry is unique. This means some comedogenic ingredients may not clog your pores. The comedogenic rating of an ingredient is not necessarily applicable to an entire product.

Comedogenic ratings of ingredients may change depending on the formulation of a product.

Some products with comedogenic ingredients may not clog pores at all, and vice versa.

Some products with non-comedogenic ingredients may lead to breakouts! If you are unsure, be sure to follow the patch-test steps listed above.

Further Learning

Hungry to keep learning? Read all about our complete guide to understanding an ingredients list.

Curious about why oils are in your skincare? Learn all about the different types of oils and their benefits here.

Make the most out of your SkinSort account by setting your liked/disliked ingredients. This will make your search for a non-pore clogging product much easier and save you time.