Ethoxydiglycol

A nice odorless liquid used mainly as a superior solubilizer and efficacy booster for cosmetic active ingredients such as skincare bigshot vitamin C, self-tanning active DHA or the anti-acne gold standard, benzoyl peroxide. 

Other than that it can also be used in hair care products where it gives a longer-lasting and more uniform coloring. According to a manufacturer, it might even prevent the formation of split ends.