ARTICLE Skin protection against UV radiation using thin films of cerium oxide E. Ortiz 1,* , L. Martínez-Gómez 1 , J.F. Valdés-Galicia 2 , R. García 2 , M. Anzorena 2 and L. Martínez de la Escalera 3 1 Instituto de Ciencias Físicas, Universidad Nacional Autónoma de México, Cuernavaca, Morelos 62210, Mexico. 2 Instituto de Geofísica, Universidad Nacional Autónoma de México, Coyoacán, Ciudad de México 04510, Mexico. 3 Corrosión y Protección (CyP), Ciudad de México, Mexico. Received: 30 August 2018 / Accepted: 24 January 2019 Abstract – In this work, we evaluated the efficiency of cerium oxide as sunscreen using titanium oxide as standard comparison material. Geant4 software was used to perform numerical simulation, we calculated the radiation dose that ultraviolet radiation deposits in a skin sample as a function of thin film thickness of the sunscreens. We found that in the interval between 5 and 15 nm of the thin film thickness and for wavelengths between 160 and 400 nm, cerium oxide has the potential to reduce the radiation dose more than 10% with respect to the same thickness band of titanium oxide. Using thin films of cerium oxide and titanium oxide with same thicknesses and greater than 45 nm, the difference in the attenuation of the radiation dose for both materials is less than 1%. The results lead us to propose cerium oxide as an alternative material to titanium oxide for the manufacture of sunscreens. Keywords: UV radiation / cerium oxide / sunscreen 1 Introduction The interactions between nanoparticles and cells are a crucial issue with regard to two fields: nanomedicine and nanotoxicology. Respect to the last field, one major concern with nanoparticles lies in their size, high reactivity and large surface area that allow them to interact with cell components, to interfere with the cell machinery, potentially triggering side effects and toxicity (Forest et al., 2015). Titanium dioxide (TiO 2 ) is a natural oxide of the element titanium with low toxicity; the classification as bio-inert material has given the possibility to normal-sized (> 100 nm) TiO 2 particles to be extensively used in food products and as ingredients in a wide range of pharmaceutical products and cosmetics, such as sunscreens and toothpastes (Grande and Tucci, 2016). The photocatalytic function and its ability to absorb UV radiation lead to its use as solar filter in sunscreens (Jiménez Reinosa et al., 2016). Human exposure to the TiO 2 may occur through ingestion and dermal penetration, or through inhalation route during both the manufacturing process and use. The biological effects and the cellular response mechanisms are still not completely elucidated, mechanistic toxicological studies show that TiO 2 nanoparticles predominantly cause adverse effects via induc- tion of oxidative stress resulting in cell damage, genotoxicity, inflammation, immune response, metabolic change and potentially carcinogenesis (Skocaj et al., 2011; Grande and Tucci, 2016). Cerium oxide (CeO 2 ) nanoparticles have a great potential application as nanofiller due to its high surface area and quick transformation between Ce þ3 ↔ Ce þ4 which enhance its antioxidant properties (Krishnamoorthy et al., 2014). Chigurupati et al. (2013) report that topical application of water soluble CeO 2 nanoparticles accelerates the healing of full-thickness dermal wounds in mice by a mechanism that involves enhancement of the proliferation and migration of fibroblasts, keratinocytes and vascular endothelial cells. Other works, e.g. (Thill et al., 2006; Fang et al., 2010; Pelletier et al., 2010) have shown the antibacterial activity of CeO 2 . The impact of the CeO 2 nanoparticles on human health and on the environment is not fully elucidated; Forest et al. (2017) showed that in vitro toxicity depends on the morphology of the CeO 2 nanoparticles, they found that, unlike cubic/octahedral nanoparticles, rod-like nanoparticles significantly and dose- dependently enhanced pro-inflammatory and cytotoxicity responses. The ultraviolet (UV) spectrum has been conveniently divided in UVC with wavelengths from approximately 200 to 280 nm, UVB covers the spectrum from 280 to 315 nm and *Corresponding author: eortiz@icf.unam.mx Radioprotection 2019, 54(1), 67–70 © EDP Sciences 2019 https://doi.org/10.1051/radiopro/2019002 Available online at: www.radioprotection.org This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.