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 Petrolatum 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 Petrolatum near the end of a label is present in tiny amounts and matters far less than the same ingredient near the top.
About Petrolatum
It is an occlusive that forms a breathable seal to slow water loss. A pure occlusive rated 0-1 and considered non-comedogenic in practice. Fatty-acid free, so it is fungal-acne safe.
On a label it can read as Petrolatum, Petroleum Jelly, Petroleum, White Petrolatum — worth knowing when you scan an ingredient deck.
Petrolatum in makeup and skincare
It anchors heavy balms, some full-coverage sticks, and night creams. Its irritancy is rated separately at 0/5, which is low.