What it is
PEG-400 is a polyethylene glycol with an average molecular weight around 400, corresponding to roughly eight repeating ethylene oxide units. At this size it is a clear, water-soluble liquid that works as a humectant and as a solvent that helps dissolve other ingredients in a formula. It also contributes to a smooth, conditioned skin feel and can help carry actives evenly through a product.
Safety & warnings
PEG-400 is widely used and generally well tolerated. PEGs can carry trace impurities from manufacturing, so reputable suppliers purify them to meet cosmetic specifications. It is not a recognized fragrance allergen; it is water-soluble and not considered comedogenic, though it may enhance the penetration of other ingredients.
Origin & sourcing
Synthetic, produced by the polymerization of ethylene oxide.
Questions everyone asks
What does the number 400 mean in PEG-400?
It refers to the approximate average molecular weight, about 400, which corresponds to roughly eight ethylene oxide units per molecule.
Why is PEG-400 added to sunscreens?
It works as a humectant and solvent, helping dissolve other ingredients and keep the formula smooth and uniform.