A synthetic or animal-derived ingredient used as a surface treatment for cosmetic pigments in products such as mascara. Also used to coat titanium dioxide nanoparticles to keep them evenly suspended and stable in sunscreen formulations.
References for this information:
International Journal of Pharmaceutics, June 2014, pages 89-96
Principles and Practice of Photoprotection, edited by Steven Q. Wang, Henry W. Lim, page 297