Is 1,2-Hexanediol Safe?

What is it?

1,2-hexanediol is a chemical relative to the more-known propylene glycol. It's a clear viscous liquid used as a humectant, filler, solvent, preservative, thickener, and conditioning agent. It's commonly used as a replacement for parabens in cosmetic formulas. It's also used in printer ink and toner. It is a synthetic chemical created from 1-hexene. 

What are its risks? 

1,2-hexanediol is a well-known penetration enhancer, meaning that it has the ability to cross the skin's barrier and allow other chemicals along with it. (Source) 

While it's considered to have a low-toxicity (ie it doesn't make you sick or immediately kill you upon ingestion) it is broken down in the body through oxidation, a process that releases free radicals. (Source)

One study says: 

"[I]f 1,2-hexanediol enters the human body either via oral intake or through an open wound, it could have critical effects. Furthermore, upon release into the environment, 1,2-hexanediol could cause considerable damage to plants and other organisms. Therefore, further investigation of 1,2-hexanediol is required to prevent toxicity to humans and other living organisms."

1,2-hexanediol is known to be a strong eye irritant. (Source) It is not known to be a carcinogen or reproductive toxin. 

Bottom line: 

While 1,2-Hexanediol isn't acutely toxic, carcinogenic, or a reproductive toxin, it certainly isn't a beneficial ingredient that would nourish or benefit the body in any way. Metabolism of hexanediol in the body creates transient free radicals (aldehydes), although amounts are small. (Source)

1-hexene, the chemical used to create 1,2-hexanediol, is highly toxic and an acute environmental pollutant. Even a single exposure can create "narcotic effects" and respiratory tract irritation. (Source) "Inhalation may cause giddiness or incoordination similar to that from gasoline vapor. Prolonged exposure to high concentrations may induce loss of consciousness or death. (USCG, 1999)" (Source) So while 1,2-hexanediol isn't known to be an acutely toxic chemical, its precursor is.