A Comparative Study of Cerium(III) and Cerium(IV) Phosphates for Sunscreens.

Crystalline cerium(III) phosphate (CePO), cerium(IV) phosphates, and nanocrystalline ceria are considered to be promising components of sunscreen cosmetics. This paper reports on a study in which, for the first time, a quantitative comparative analysis was performed of the UV-shielding properties of CePO, Ce(PO)(HPO)(HO), and CePO/CeO composites. Both the sun protection factor and protection factor against UV-A radiation of the materials were determined. Ce(PO)(HPO)(HO) was shown to have a sun protection factor of 2.9, which is comparable with that of nanocrystalline ceria and three times higher than the sun protection factor of CePO. Composites containing both cerium dioxide and CePO demonstrated higher sun protection factors (up to 1.8) than individual CePO. When compared with the TiO Aeroxide P25 reference sample, cerium(III) and cerium(IV) phosphates demonstrated negligible photocatalytic activity. A cytotoxicity analysis performed using two mammalian cell lines, hMSc and NCTC L929, showed that CePO, Ce(PO)(HPO)(HO), and nanocrystalline ceria were all non-toxic. The results of this comparative study indicate that cerium(IV) phosphate Ce(PO)(HPO)(HO) is more advantageous for use in sunscreens than either cerium(III) phosphate or CePO/CeO composites, due to its improved UV-shielding properties and low photocatalytic activity.