Propylene glycol is a humectant, which means that it is an ingredient that is added to cosmetics to increase moisture retention in skin and hair.

Propylene glycol is well tolerated by the skin and shouldn’t cause redness or irritation. However, the potential problem with propylene glycol is that it is a penetration-enhancing humectant.

Humectants absorb moisture from anything around them and if your skin care contains a penetration-enhancing humectant, it can mean that harmful toxins may be able to permeate the skin where they would not normally be able to.

If these molecules are skin toxins like pollutants or harsh chemical ingredient, they could harm the lipid barrier and cause skin irritation.