An organic molecule with two alcohol groups, used in cosmetics as a humectant to bind moisture and hold water to the skin. Alcohols are attracted to water; the smaller alcohols evaporate quickly, drawing water away from the skin, while larger organic alcohols do not evaporate as quickly and actually hold water to the skin.
As printed in the Journal of the American College of Toxicology, butylene glycol is "safe as presently used in cosmetics." The report goes on to say that repeated insult patch tests on butylene glycol produced no evidence of skin sensitization. Nevertheless, on the internet a lot of critisism can be found, stating it can cause liver and kidnet damage. There is absolutely no reason for this. Paula Begoun, the American self-called Cosmetic Cop also states:
"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 (Material Safety Data Sheets) are talking about these risks when 100% concentrations of the substance is used. Even water and salt have frightening comments regarding their safety according to their MSDSs. In cosmetics, propylene glycol is used only in 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, it is not a concern in the least. Women are not suffering from liver problems because of propylene glycol in cosmetics."
Therefore a lot of manufacturers utilizes small amounts of butylene glycol to benefit their formula(s) and to provide skin conditioning and moisturizing properties to the skin. With the ingredient data currently available, you can be confident in the safe and effective use of this ingredient.