Polyethylene glycols (PEGs) are petroleum-based compounds that are widely used in cosmetics and contain potential toxic impurities.
If you look at the ingredients list of many conventional skin care products, you may see the prefix PEG followed by a number, such as PEG-4 or PEG-100. These numbers correlate to how many units of ethylene glycol they comprise and the lower the number, the more easily the compound is absorbed into the skin.
PEGs may be contaminated with carcinogens ethylene oxide and 1,4 dioxane. To stay happy and healthy, avoid ingredients with PEG as a prefix.