Butylene glycol is rapidly absorbed through any tissue, including the skin. It is rapidly metabolized to gamma-hydroxybutyric acid in animals and humans. Gamma-hydroxybutyric acid is a naturally occurring chemical found in the brain and peripheral tissues of humans. Gamma-hydroxybutyric acid is also rapidly metabolized into succinate through the tricarboxylic acid cycle within the body. Given in high doses, a neuromodulator effect can be seen. However, in the small doses used as a solvent in pharmaceuticals and nutritionals, there are no known side effects. In water-based products, a concentration of 0.5% butylene glycol, as a solvent, would be safe for topical use.
Butylene glycol in concentrations of 0.5% or less in a topically applied product scores at least 9 out of 10, with a score of 10 being perfectly safe.
Anyone know if there's ever been a study of the ratio of (1,3) butanediol to (1,4) butanediol in common make-up products? My money says that the proportion of (1,4) would turn out to be higher than naturally tends to occur via normal synthesis techniques.
The dirty little secret of the cosmetics industry: foundation is actually a time-release formulation of GHB.
The new fashion in getting high: vacuum distillation of cosmetics products.