Often, PEGs are connected to another molecule. You might see, for example, "PEG 100 stearate" as an ingredient. What this means is that the polyethylene glycol polymer with an approximate molecular weight code of 100 is attached chemically to stearic acid.
Now just to clear up a few misperceptions... PEGs are not found in anti-freeze; that's ethylene glycol, NOT polyethylene glycol. And yes, PEGs are found in some spray-on oven cleaners, but those PEGs are quite different in both molecular weight and structure than the PEGs found in your cosmetics. They are also used in pharmaceuticals as laxatives, again with a different molecular weight.
So, are PEG's something you want or don't want in your skin care products? The answer isn't really a simple yes or no.
I quote from the "Safety assessment on polyethylene glycols (PEGs) and their derivatives as used in cosmetic products,” study by Toxicology and Preclinical Affairs, 2005.
"The PEGs produce little or no ocular or dermal irritation and have extremely low acute and chronic toxicities. They do not readily penetrate intact skin, and in view of the wide use of preparations containing PEGs, only a few case reports on sensitization reactions have been published, mostly involving patients with exposure to PEGs in meds, or following exposure to injured or chronically inflamed skin. On healthy skin, the sensitizing potential of these compounds appear to be negative.”
The most important thing you need to know about PEGs is that they have a penetration enhancing effect and are found in many, many skin creams. The penetration enhancing effect is important for three reasons: 1) If your skin care product contains a bunch of other undesirable ingredients, PEGs will make it easier for them to get down deep into your skin. 2) By altering the surface tension of the skin, PEGs may upset the natural moisture balance. 3) PEGs are not always pure, but often come contaminated with a host of toxic impurities.
While the penetration enhancement is dependent upon a number of factors, most important is the overall health of the skin. PEGs of all sizes may penetrate through injured skin with compromised barrier function. So it is very important to avoid products with PEGs if your skin is not in tip-top condition.