Prop ylene Glycol
Propylene glycol (along with other glycols and glycerol) is a humectant or humidifying and delivery ingredient used in cosmetics, meaning it helps other ingredients absorb better into the skin. Despite research to the contrary, you can find Web sites and spam e-mails stating that propylene glycol is really industrial antifreeze and the major ingredient in brake and hydraulic fluids. These sites also state that tests show it to be a strong skin irritant. They further point out that the Material Safety Data Sheet (MSDS) on propylene glycol warns users to avoid skin contact because systemically (in the body) it can cause liver abnormalities and kidney damage.
As ominous as that sounds, it is so far from the reality of cosmetic formulations that almost none of it holds any water or poses real concern. It is important to realize that the MSDS sheets are talking about 100% concentrations of a substance. Even water and salt have frightening comments regarding their safety according to their MSDS reports. It is true that propylene glycol in 100% concentration is used as antifreeze, but—and this is a very big but—in cosmetics it is used in only the smallest amounts to keep products from melting in high heat or freezing when it is cold. It also helps active ingredients penetrate the skin. In the minute amounts used in cosmetics, propylene glycol is not a concern in the least. Women are not suffering from liver problems (as some Web sites have asserted) because of propylene glycol in cosmetics.
Source @ Hot Shaper