Protection from solar radiation is usually achieved by the use of UV organic absorbers, often combined with inorganic materials such as TiO₂ or ZnO₂. These compounds are either dispersed in lotions or in films. Whereas lotions are commonly known for skin protection, films cannot be used as sunblock. The reason is here, that in films free radicals emerge from the UV absorption, which are very toxic to cells.

Hernán Míguez, University of Seville, Spain, and colleagues designed an alternative film, which very effectively shields from UV-radiation without any absorption process but by reflection, hence, also allowing an application on the skin. 1D photonics crystals, which consist of overlaying sheets of ZrO₂ and SiO₂ or TiO₂ and SiO₂ particles are stacked and embedded by a biocompatible polymer. The refractive indexes of each layer can be controlled during fabrication, enabling the production of multilayer structures, where the refractive index changes periodically.

This type of arrangement induces optical interference effects, that reflect radiation in a certain range of wavelength. Hence, the films are transparent to visible light but efficiently block UV light solely by reflection.

• Biocompatible Films with Tailored Spectral Response for Prevention of DNA Damage in Skin Cells,
  Rebeca Núñez-Lozano, Belén Pimentel, José R. Castro-Smirnov, Mauricio E. Calvo, Hernán Míguez, Guillermo de la Cueva-Méndez,
  Advanced Healthcare Materials 2015.
  DOI: 10.1002/adhm.201500223