Skin Care: Propylene Glycol

Every one has something that just gets under their skin. For me, it's spreading myths and misinformation about harmless chemicals. Over the past couple of months I have been working on an all natural skin care line for my company. All natural cosmetics are not at all important to me, I'm much more concerned about making skin care products that don't contain irritating ingredients, have ingredients with proven research for their benefits and are well formulated products. However, natural is the buzz word, and I've got to earn my paycheck.

Ecocert guidelines prohibit the use of glycols because they are derived from petroleum. Well Bossman talked to a supplier who had an Ecocert approved Propylene Glycol and he ordered a sample of it. I should mention Bossman is not a chemist, he's a meteorologist  He started in QC, moved to R&D then to manager. His chemistry knowledge is fairly limited. So he handed me the literature for the Ecocert Propylene Glycol and I looked it over and found that the INCI was propanediol. Propylene Glycol exists as two stereoisomers.

1,2-propanediol:

1,3-propanediol:

The difference between the molecule is which carbon the second -OH group is bonded to. Standard propylene glycol is a raecemic mixture (equal parts) of the two isomers. The Ecocert propanediol is stereospecific to the 1,3-propanediol. Bossman and I got in to a big disagreement about this because he would not accept that the propanediol was not (for all intents and purposes) the same as the propylene glycol that we use every day. There are minor differences but they serve the same purpose and have essentially the same properties, especially for our products. So I did some research on exactly why customers felt we needed to avoid propylene glycol in cosmetics. I was truly surprised at what I found people saying about poor little propylene glycol.

This site claims the propylene glycol is  linked to cancer, developmental/ reproductive issues, allergies/ immunotoxicity, neurotoxicity and endocrine disruption. It has been found to provoke skin irritation and sensitization in humans as low as 2% concentration, while the industry review panel recommends cosmetics can contain up to 50% of the substance. It goes further and claims that it alters the structure of the skin by allowing chemicals to penetrate deep beneath it while increasing their ability to reach the blood stream. Even the EWG (which I should mention, I hate, because they are fear mongers) isn't that extreme. They only list propylene glycol as a 3 (moderate hazard) and claim that it is a skin sensitizer. Honestly it's just absurd. 

Propylene glycol is a humectant, which means it draws water to your skin, acting as a moisturizer. It also improves freeze/ thaw stability of finished products by preventing them from freezing as hard. It is classified by the FDA as GRAS (generally recognized as safe) for all food applications. Unlike it's cousin, ethylene glycol, propylene glycol is easily metabolized by the liver and it does not accumulate in the body over time. The acute oral toxicity of propylene glycol is very low, ingestion of large quantities in a very short period of time are required to achieve a toxic concentration in the blood. I could not imagine a situation in which a cosmetic formula would use 50% propylene glycol as the first website mentioned, it's usually used at around 2-3% in a finished lotion formula. Prolonged contact with propylene glycol is essentially non-irritating to the skin. Undiluted propylene glycol is minimally irritating to the eye, and can produce slight transient conjunctivitis (the eye recovers after the exposure is removed). Exposure to mists may cause eye irritation, as well as upper respiratory tract irritation. Inhalation of the propylene glycol vapors appears to present no significant hazard in ordinary applications. Both experimental and anecdotal evidence to date indicate propylene glycol to be completely non-carcinogenic. In a very interesting study, some 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. 

There is simply an overwhelming amount of evidence that indicates that propylene glycol is a perfectly safe ingredient for all food and cosmetic applications. The Agency for Toxic Substances and Diseases Registry issued this statement regarding propylene glycol. Unless you are one of the very few people with an allergy to propylene glycol, it's just not something to be concerned about.