Titanium dioxide and zinc oxide nanoparticles in sunscreens: focus on their safety and effectiveness.

Title	Titanium dioxide and zinc oxide nanoparticles in sunscreens: focus on their safety and effectiveness.
Authors	Threes Smijs, Pavel
Magazine	Nanotechnology, Science and Applications
Date	10/01/2011
DOI	10.2147/NSA.S19419
Introduction	Sunscreens are critical in protecting skin from harmful ultraviolet (UV)B (290-320 nm) and UVA (320-400 nm) radiation. The United States Food and Drug Administration mandates that the UVA protection factor should comprise at least one-third of the total sun protection factor. Titanium dioxide (TiO2) and zinc oxide (ZnO) are commonly used inorganic physical sun blockers, with TiO2 being more effective against UVB and ZnO against UVA. This combination provides adequate UV protection. To address the cosmetic issue of opacity in sunscreens, microsized TiO2 and ZnO have been increasingly replaced by nanoparticles (NPs) of these minerals (<100 nm). This review highlights the impact on UV attenuation when replacing microsized particles with NPs and assesses the physicochemical factors influencing NP sunscreen effectiveness and safety. While the use of TiO2 and ZnO NPs eliminates opacity, it can disrupt the necessary balance between UVA and UVB protection. Combining micro- and nanosized ZnO dispersions with nanosized TiO2 particles could enhance this balance. Skin exposure to NP-containing sunscreens results in TiO2 and ZnO NPs integrating into the stratum corneum, potentially altering NP attenuation properties through interactions between particles, skin, and light. Both sunscreen NPs can induce (photo)cyto- and genotoxicity, occasionally penetrating viable skin layers, particularly with prolonged exposure and ZnO. Photocatalytic effects, most pronounced in anatase TiO2, are not entirely preventable by particle coatings, although silica-based coatings are the most effective. Caution is advised in developing new sunscreens, with emphasis on NP stabilisation, chronic exposure assessment, and minimising free-radical production.
Quote	Threes Smijs and Pavel. Titanium dioxide and zinc oxide nanoparticles in sunscreens: focus on their safety and effectiveness. Nanotechnology, Science and Applications. 2011. DOI: 10.2147/NSA.S19419
Element	Titanium (Ti) , Zinc (Zn)
Materials	Oxides
Industry	Pharmaceuticals & Cosmetics