What is PEG-400?
PEG-400 (INCI name: PEG-8) is a solvent. 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.
You may see it on labels as Peg 400, Peg-400, Polyethylene Glycol 400, Polyethylene Glycol, so it can hide under more than one name in an ingredient list.
Where PEG-400 shows up
You'll most often find PEG-400 in toners, nail products, and cleansing formulas. Separately from clogging, its irritancy is rated 0/5 — low, so it's unlikely to sting or sensitise on its own.
Is PEG-400 bad for acne-prone skin?
Because it barely registers on the comedogenic scale, PEG-400 is generally a safe pick for breakout-prone skin and is often recommended as a gentler alternative to heavier ingredients.