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 Propylene Glycol 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 Propylene Glycol near the end of a label is present in tiny amounts and matters far less than the same ingredient near the top.
About Propylene Glycol
It is a humectant that pulls water into the upper layers of skin. A humectant and penetration enhancer rated 0/5 for clogging. Can be mildly irritating for some at high levels.
Propylene Glycol in makeup and skincare
It is a near-universal hydrator in primers, foundations, toners, and moisturisers. Its irritancy is rated separately at 2/5, which is low.