What a 1/5 rating means
On the comedogenic scale, a 1 sits at the safe end of the scale — clogging is unlikely for most people. That places D&C Red #9 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 D&C Red #9 near the end of a label is present in tiny amounts and matters far less than the same ingredient near the top.
About D&C Red #9
It is a cosmetic colorant that gives makeup its shade. A barium lake pigment used in colour cosmetics. Rated 1, grouping it with the low-risk reds rather than the 3-rated 17, 21 and 3.
On a label it can read as D&C Red 9, D&C Red #9, D C Red 9, Ci 15585:1 — worth knowing when you scan an ingredient deck.
D&C Red #9 in makeup and skincare
It is the shade in lipsticks, blushes, and other colour cosmetics. Its irritancy is rated separately at 0/5, which is low.