What a 0/5 rating means
On the comedogenic scale, a 0 means it will not clog pores for essentially anyone, including very acne-prone skin. That places Carbomer in the range most people, including many with acne-prone skin, tolerate well.
One thing the number cannot tell you is concentration. Ingredients are listed in descending order, so Carbomer near the end of a label is present in tiny amounts and matters far less than the same ingredient near the top.
About Carbomer
It is a thickener that controls how a product flows and feels. A synthetic gelling polymer rated 0/5, used to thicken serums and gels.
On a label it can read as Carbomer, Sodium Carbomer, Acrylates Copolymer — worth knowing when you scan an ingredient deck.
Carbomer in makeup and skincare
It sets the consistency of gels, liquid foundations, and serums. Its irritancy is rated separately at 1/5, which is low.