Zinc oxide and titanium dioxide nanoparticles (smaller than 100 nanometers) are safe for skin application because they don't absorb through skin. The trade-off: they're made smaller for better cosmetic feel, but this raises inhalation concerns with spray formulas. Environmental risk is currently low, though it could shift as usage increases.

This was a literature review published in a peer-reviewed dermatology journal, synthesizing existing research on how these mineral UV filters work, whether they penetrate skin, and their safety profiles.

Funding not disclosed in abstract