Titanium dioxide is a physical sunscreen protecting against UVB and short UVA (a.k.s. UNA-1) light. It has a long history of seemingly safe use and is not irritating. Its disadvantages include unsightly whitish tint and insufficient protection against long UVA (a.k.a UVA-2).

It may also help generate harmful free radicals via photocatalytic mechanism when exposed to sunlight. These effects may not have significant impact in topical use but the issue needs to be researched.

Nanoparticle forms of titanium dioxide are less unsightly but their potential risks are unclear and may be greater than those associated with regular forms. Regular titanium dioxide is highly stable under most conditions. However, it has some photocatalytic activity (i.e. promotes reactions between other chemicals), especially in direct sunlight. Titanium dioxide nanoparticles appear to have much greater photocatalytic activity than regular titanium dioxide powder and might trigger formation of harmful free radicals when exposed to sunlight. Most manufacturers of titanium dioxide nanoparticles coat them to reduce or eliminate such effects.

To increase protection and extend its range, titanium dioxide is usually combined with chemical UVB and UVA blockers and/or zinc oxide.