What does comedogen mean?
An ingredient can be called comedogenic if it has the property of clogging pores, i.e. sebaceous glands, and thus causing blackheads to form; this is referred to as the comedogenicity of an ingredient. This may cause or aggravate impurities and acne. The conclusion is that oily skin and impure skin in particular should not come into contact with these substances which are considered to be comedogenic and that products containing these substances should be avoided - this is the assumption.
But where does the attribution of comedogenicity actually come from? A look back helps here: In the 1950s, cosmetic products were tested which were supposed to have a pore-clogging effect. For this purpose, they were applied to the ears of rabbits because rabbit ears react particularly sensitively and it was waited whether the rabbit ears developed blackheads. These findings were then transferred to the human skin. Apart from the animal welfare aspect, such a procedure is of course questionable.
The comedogenicity ranking according to Dr. Kligmann
Another attempt to evaluate the comedogenic properties of a cosmetic substance was made in the 1970s. The dermatologist Kligmann together with his partner tried to find out which cosmetic products trigger acne. Within the scope of the so-called Kligmann protocol they wanted to rate the comedogenicity of a substance on a scale between 0 and 5 (5 is very bad) which was supposed to be responsible for the development of acne. Ranking lists with ingredients which were considered to be comedogenic were created.
Unfortunately, these results on comedogenicity were not very helpful either, as they varied from test to test. Furthermore, the acne did not decrease if the ingredients classified as comedogenic were simply left out. In fact, acne did improve when these "problematic" comedogens were kept but combined with vitamin A acid (a classic anti-acne ingredient).
Persistent but useless: comedogenicity today
Today, it has long been clear that it is not a single ingredient that is classified as comedogenic, but the entire formulation of a product that determines whether a product triggers or aggravates blemishes and acne. If you only look at a single ingredient such as coconut oil, shea butter or acetylated lanolin alcohol, then it may very well be comedogenic. However, the conclusion that the entire product is also comedogenic is simply wrong. Rather, it is important to look at the concentration of the ingredient - the less of it there is, the less likely it is to trigger acne. If you were to theoretically use the pure form of a comedogenic substance, it would certainly be pore-clogging.
However, if you take a look at the INCI lists of today's cosmetic products, you will find out that they consist to a large extent of completely different ingredients and that the substance designated as comedogenic occurs in such a diluted form that it simply cannot have a comedogenic effect anymore. So, if you have blemished skin and want to combat it, it's better to focus on ingredients that work against acne and get recommendations for products that are right for your skin's condition, rather than focusing on a single substance labeled as comedogenic. This doesn't mean that you won't have to change a product once in a while because you can't handle it. However, this is most likely due to reasons other than a supposed comedogenic ingredient.