Ah, propylene glycol. The tiny little ingredient lurking in your moisturizer, serum, makeup, deodorant, shampoo, and approximately 47 other things you have in your bathroom right now. Nobody puts propylene glycol on the front of the bottle. Nobody is standing in Sephora screaming, “OH MY GOD, THEY PUT PROPYLENE GLYCOL IN THIS!” And yet, this humble little molecule is doing a surprising amount of work behind the scenes. It helps products hold onto water. It helps ingredients dissolve. It can improve how certain ingredients move through the outer layers of skin. It can affect texture and feel. It can even