This is the next instalment in our ongoing series about chemicals often found in home and personal care products. Here, we make an assessment of ingredients, so you can make informed choices about the products you buy.
Today, we’re looking at propylene glycol.
What is propylene glycol?
Propylene glycol is a colourless and nearly odourless liquid with a slightly sweet taste.
It is traditionally a petroleum derivative. But today, propylene glycol is also available as a biobased derivative of 100% renewable resources like yeast, corn, vegetable oils, and miscellaneous carbohydrates. Most propylene glycol is, however, still the synthetic petrochemical kind.
What is propylene glycol used for?
Propylene glycol is incredibly versatile — in just one product, it can have a variety of functions. It is also relatively cheap. For these reasons, propylene glycol is valuable in many industries.
It is a humectant, which means that it attracts and locks in moisture via absorption. This is why you will find propylene glycol in moisturisers, hair styling products, wrinkle fillers, and such.
It is also an emulsifier and a solvent for things like food colours, flavours, and fragrances. Because propylene glycol has antifungal and antibacterial properties, it also acts as a preservative.
What kind of products contain propylene glycol?
Propylene glycol is an ingredient in many food products, medicine, supplements, and other edible items like liquid sweeteners.
You’ll find it in the ingredient lists of personal care products like antiperspirants, deodorants, shaving creams, hand sanitisers, body lotions, moisturisers, conditioners, shampoos, and sunscreens. It is also in things like paints, varnishes, polyurethane cushions, plastics, and tobacco products.
The e-liquid used in electronic cigarettes and the artificial smoke or fog used in theatrical productions both contain propylene glycol.
You may have heard that propylene glycol is a main ingredient in antifreeze. This is true. The chemical lowers water’s boiling point, which is why it is an active ingredient in antifreeze and in aircraft deicing fluid.
However, there are a lot of misconceptions about propylene glycol. Because of its association with antifreeze, many think that it is a harmful ingredient. But antifreeze contains the more concentrated industrial grade propylene glycol. What we are concerned with here is the food grade and cosmetic grade kind.
Is propylene glycol safe?
This is what cosmetic chemist Tonya McKay has to say about propylene glycol:
“Unlike its dangerous and frequently lethal cousin, ethylene glycol, [propylene glycol] is easily metabolised 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 [propylene glycol] is excreted directly from the body and never even comes into contact with the liver.”
Propylene glycol is in the US Food & Drug Administration's “Generally Recognised as Safe” list, which means that it is deemed safe for use as an additive in food. However, the European Union has not approved the chemical's use as a general purpose food additive.
EWG gives the chemical a score of 3 and an overall hazard rating of low to moderate. The group reports that propylene glycol is not likely to be a developmental or reproductive toxicant. However, it may cause skin irritation. The EWG Cosmetics Database notes that the chemical is associated with allergic contact dermatitis and contact urticaria, and that these were observed with concentrations of as low as 2%.
Still, the Cosmetic Ingredient Review Expert Panel found that propylene glycol is safe for use in cosmetic products at concentrations not exceeding 50%.
Propylene glycol is EcoCert certified and is recognised by Australian Certified Organic, which uses the COSMOS raw materials database. NATRUE has not approved the chemical’s use in natural and organic cosmetics.