Skim through

What it does: moisturizer/humectant, solvent, viscosity controlling, conditioning

The science

Propylene glycol is a colorless liquid. Its main job is to improve the 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 propylene glycol include being a humectant (helps hair attract water), being a solvent for other ingredients and being a penetration enhancer, meaning it can help other ingredients to penetrate the skin better.   

It also absorbs excess water in a formula, reducing bacteria growth to help your products last longer.

Benefits for your hair

Promotes hydration and smoothness

Propylene glycol helps the skin and hair absorb and retain moisture. It also forms a protective layer on the scalp, preventing moisture from escaping. More hydration softens and smoothens the hair, making it easy to detangle.

TLDR 

Propylene glycol hydrates and smoothens the hair, making it easier to detangle. It helps increase the shelf life of products and helps penetration.