- It's a helper ingredient that improves the freeze-thaw stability of products
- It's also a solvent, humectant and to some extent a penetration enhancer
- It has a bad reputation among natural cosmetics advocates but cosmetic scientists and toxicology experts do not agree (read more in the geeky details section)
Propylene Glycol (PG) is a colorless liquid, whose main job, usually, is to improve the so-called freeze-thaw stability of the products. This means that it makes sure that a product doesn’t freeze or melt in low or high temperatures. To achieve this, small amounts - usually less than 2% - is used.
Other functions of PG include being a humectant (helps skin attract water), being a solvent for other ingredients and being a penetration enhancer.
If you google PG or you like to read around on sites advocating natural cosmetics you might have read some really scary info about this ingredient. The two most common accusations are that it’s a strong skin irritant and that it modifies the skin to allow toxins to penetrate it.
As for the first one, yes PG can be a skin irritant if used 100% on your skin, but so can many things in their pure, 100% form. Think about salt. It’s not the same if you try to eat it in itself or if you put a pinch of it on your food. So PG used in small amounts in cosmetics is just fine according to every credible scientist and toxicology expert.
As for the second thing (that PG allows toxins to get through our skin) it is somewhat true that PG might help some ingredients to penetrate the skin better. But it does not work so that a tiny amount of PG allows all the bad stuff to go right into our blood. English cosmetic chemist, Colin wrote a very good post about this. He writes that the skin is very good at keeping things out and getting some good ingredients into it is actually not easy. According to his experience PG is not a very good penetration enhancer and fairly large (10-25%) amount is needed for this function. But more than 10% can be irritating, so it’s very rare that a cosmetic product contains this large amount.
The scientists at the Beauty Brains are even more accepting of PG. They write that PG is safe for ingestion (it can be a food additive!) AND safe for use in injected drugs, so it’s unlikely to cause any problems in a topical cosmetic product applied on intact skin.
All in all, PG is a helper ingredient and is not especially good for your skin. But used in small (<5%) amounts it’s absolutely fine, not poisonous and there is no reason to be afraid of it.