From Nano to Micro: Unraveling the Role of Particle Size in TiO₂ Toxicity and Biocompatibility

The use of UV filters is a well-established strategy for preventing skin cancer and photoaging. Among inorganic filters, titanium dioxide (TiO2) provides excellent protection against both UVA and UVB radiation. Moreover, the use of such inorganic filter at the nanosized scale has increased their acceptability because it ensures the cosmetically desired transparency in sunscreens that consumers demand. However, concerns remain regarding the potential toxicity of TiO2 nanoparticles and discussion about its use in pharmaceuticals and cosmetics is still in progress. Their increased (bio)reactivity compared to bulk materials may lead to DNA damage, and their ability to penetrate dermal, respiratory, or gastrointestinal barriers is still under discussion. For this reason, the present study is focused on comparing the toxic behavior of two commercially available titanium (IV) oxides, one at the microscale and the other at the nanoscale. First, the morphology and hydrodynamic diameter of the TiO2 nanoparticles were characterized. Then, potential interactions and/or interferences of these nanoparticles with the methods used to evaluate cytotoxic behavior were studied. Finally, the hemocompatibility, cytotoxicity, phototoxicity and genotoxicity of both micro- and nano-sized TiO2 were evaluated using human keratinocytes.