Butylene Glycol:

Butylene Glycol is an organic chemical, a diol. It is added to skin care products to increase penetration by other ingredients in the formulation, thin the consistency, and make it easier for other ingredients to mix.  It also has humectant properties that hydrate cells and helps ease the appearance of wrinkles.

Can be found in the following O Naturals Products: Nourishing Watermelon & Vitamin C Gel Face Mask Anti-Aging Kiwi & Vitamin E Gel Face Mask, Antioxidant Lemon & Vitamin B Face Mask