An interesting fact about propylene glycol is that it is non-toxic when ingested even in reasonably large amounts. Unlike its dangerous and frequently lethal cousin, ethylene glycol, PG is easily metabolized by the liver into normal products of the citric acid metabolic cycle, which are completely nontoxic to the body. Approximately 45 percent of any ingested PG is excreted directly from the body and never even comes into contact with the liver. The elimination half-life for propylene glycol is approximately four hours, and there is no bioaccumulation (buildup in the body over time). A few rare incidents have occurred where a person ingested a large quantity of propylene glycol and suffered some liver and neurological effects as a result, but these were short-lived and subsided once the material was metabolized and excreted.
Metabolic Cycle for Propylene Glycol:
Propylene glycol → lactic acid → pyruvic acid → CO2 + water
Both experimental and anecdotal evidence to date indicate PG to be completely non-carcinogenic, despite its “petroleum-based” origin. In a very interesting study, some unfortunate rats were fed propylene glycol at amounts equal to 5% of all of their food intake every day for two years, which is a pretty huge volume over a large portion of their lifetime. There were no observable effects on their health or behavior.
Another frequently cited concern about propylene glycol is its use as a component of antifreeze, especially in applications such as the airline industry for de-icing wings and runways. Many of the articles I have found online make a point to highlight the fact that PG is “antifreeze,” a term which has many negative connotations in the minds of people who have heard of the significant and potentially fatal dangers of “antifreeze.” This reputation is well-deserved for ethylene glycol, an extremely toxic material that was commonly found in automotive and other antifreeze solutions. However, propylene glycol has become a common replacement for ethylene glycol in many commercially available antifreeze formulations because it is much safer than ethylene glycol.
Propylene Glycol
Another relevant point is that the word “antifreeze,” frequently used to alarm consumers, is simply a scientific term used to describe a completely innocuous process — the lowering or depression of the freezing point of a liquid. An example of this process is the application of salt to roads and walkways in a snow storm. This helps melt snow and ice and prevent development of dangerous icy conditions. The salt accomplishes this by lowering the freezing point of water. This is an example of a “safe” chemical being used as antifreeze. My point here is to not be alarmed by the term antifreeze or by the chemical, propylene glycol. While few chemicals are entirely without risk, propylene glycol is considered to be safe at the low concentrations used in personal care products and even food products.
What is propylene glycol used for in personal care products?
It is a very effective humectant
It is a solvent or carrier agent for fragrances and preservatives.
It can be used as an emulsifier or co-surfactant.
It is used as a solvent for pigments in cosmetics.
It can be used as a preservative due to its anti-fungal and anti-microbial properties.
It is frequently used in deodorants and antiperspirants.
It is found in hand cleansers and disinfecting gels.
It is a common additive in shaving creams and gels.
