DIPROPYLENE GLYCOL: Dipropylene Glycol (DPG) is a small molecular weight synthetic solvent which is colourless and odourless.
There are two main usage in cosmetic industry where first is it commonly used in perfumes and fragrances as a carrier and a diluent (compound that is used as a diluting agent). By mixing this with the fragrance oil, one can adjust the strength of the fragrance by adjusting the ratio of the oil and DPG. DPG also helps in making the fragrance disperse slower such maintaining longer lasting smell.
The DPG is also often use as a viscosity decreasing agents in cosmetics and skincare products for manufacturer to achieve desired viscosity of the product.
It is worth to watch out for this ingredient if you have sensitive skin or looking for cosmetic to be used around the eye as CIR (Cosmetic Ingredient Review) has indicated that this can be an irritant on the skin and around the eye.
Fragrance Ingredient as a Solvent, carrier
Viscosity Decreasing Agent