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 PEG-400 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 PEG-400 near the end of a label is present in tiny amounts and matters far less than the same ingredient near the top.
About PEG-400
It is a solvent used to dissolve other ingredients or aid drying. A low-molecular-weight polyethylene glycol used as a water-soluble solvent and humectant. Rated 1 on the Fulton-derived table; PEGs in this size range are generally well tolerated on acne-prone skin.
On a label it can read as Peg 400, Peg-400, Polyethylene Glycol 400, Polyethylene Glycol — worth knowing when you scan an ingredient deck.
PEG-400 in makeup and skincare
It is used in liquid liners, nail products, and some cleansers. Its irritancy is rated separately at 0/5, which is low.