If you think an ingredient might cause acne then you will have seen the ingredient busting comedogenic charts & tools available on the internet and perhaps even decided a products fate using them - look at the product INCI, look up the ingredient on chart and BAM! if it has highly comedogenic ingredients, it will cause acne, if it doesn’t, then it won’t. For the complex problem of acne causation this clear, simple answer is, probably wrong.
Why? The comedogenicity scale of 0 (fine) to 5 (danger ahead) came from academic models (simplified stuff) rather than real world usage (really complex stuff). Normally, a model is pretty good at predicting the real world but for comedogenicity ratings, its flawed. We humans as test subjects are too variable to be reliably used and so, typically, we test a rabbit ear as it's quicker and easier. Take one rabbit, apply product X to its sensitive inner ear & see if the pores clog. Perfect for Rabbit makeup. Not much use for our less sensitive human skins though - ingredients that are non-comedogenic on us are comedogenic for our sensitive Benjamin Bunny. But it at least gives us an indication though, right? Nope. A comedogenic ingredient in isolation might not be comedogenic in a product because dilution decreases comedogenicity. An example - Acetylated lanolin alcoho is strongly comedogenic (4/5) at 100% becomes non-comedogenic (CR-1) after dilution to 25%. Now most non-serums are at least 80% water so how much effect is that one ingredient having? And (let's really bend the Matrix Spoon here) even if a product contains no comedogenic ingredients, it can still be comedogenic on the skin because ingredients can combine - or it can go the other way. Now let's throw in comedogenicity is also partially determined by your unique skin chemistry and the variance of a batch chemical during production and "you cannot determine from a reading of the ingredients whether a given product will be acnegenic or not" - those were the words of Dr Kligmanm, the man who invented the comedogenic scale. So what can you do?
TRUST YOUR OWN EXPERIENCES. If the product has *lots* of comedogenic (4-5 rating) ingredients high up on the ingredients list perhaps give it a miss. If it has one, patch test it and see - real world experiences beat internet list-based hazy guesses
TRUST YOUR OWN EXPERIENCES. If you’re breaking out within a month of using a product, check for severely comedogenic (4-5 rating) ingredients high up on the ingredients list (so higher concentration) as a starting point (this doesn't mean they are to blame - do you have other products which have them and don't cause breakouts?)
TRUST YOUR OWN EXPERIENCES. Patch test everything, especially natural oils and butters which are undiluted.
So in summary - TRUST YOUR OWN EXPERIENCES What shouldn't you do?
Use comedogenicity ratings as a lazy way to avoid patch testing new products.
Witch hunt products or make wild predictions of suitability based on a comedogenic scale you saw.
Not buy a product just because it contains a comedogenic ingredient - especially if it's low down in the ingredient list (think dilution)
Assume an oil undiluted acts the same as an oil in a formulation, it doesn't as there’s no straightforward relationship (fatty acids are chemically bound in a formulation making them behave very differently).