PEG

PEG stands for polyethylene glycol. PEG comes in a variety of forms, including PEG-4, PEG-8, PEG-14, PEG-20, PEG-32, PEG-75, PEG-100, PEG-150, and PEG-200.

What are the benefits?

PEGs are compatible with a wide variety of ingredients and are used in the formulation as emollients, emulsifiers, and penetration enhancers. 

PEG's safety in its various forms has recently been called into question. The main concern is that they may contain harmful impurities including ethylene oxide and 1,4 dioxane. Both of these are by-products of the manufacturing process and are not inherent in any type of PEG. While this was once a problem, reputable cosmetic product manufacturers have long since removed these impurities from the finished ingredient, making PEGs skin-safe.

Most of the studies done on PEG to date has shown PEG to be non-irritating to skin or eyes, even at concentrations higher than what most cosmetic products contain. PEGs are also commonly regarded as non-toxic due to their inability to penetrate intact skin. However, as with even the gentlest products, the risk of discomfort increases when skin is inflamed or damaged.

See also:
Emollient
Emulsifier

Ref:
Fruijtier-Pölloth C. Safety assessment on polyethylene glycols (PEGs) and their derivatives as used in cosmetic products. Toxicology. 2005 Oct 15;214(1-2):1-38. doi: 10.1016/j.tox.2005.06.001. PMID: 16011869.