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 Niacinamide 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 Niacinamide near the end of a label is present in tiny amounts and matters far less than the same ingredient near the top.
About Niacinamide
It is an active ingredient included for a specific skin benefit. Vitamin B3, an oil-regulating active rated 0/5. Non-comedogenic and often recommended for acne-prone skin.
On a label it can read as Niacinamide, Nicotinamide, Vitamin B3 — worth knowing when you scan an ingredient deck.
Niacinamide in makeup and skincare
It is formulated into targeted treatments and some makeup-skincare hybrids. Its irritancy is rated separately at 0/5, which is low.