Practically all grades of Titanium dioxide used as UV filters in sunscreens are technically classed as nanoparticles as the individual particles measure less than 100nm across. There are two concerns over the use of nanoparticles in cosmetics - firstly that they cause the formation of free-radicals when exposed to UV light and secondly that they can penetrate the skin and enter the body.
To avoid the first problem, the Titanium dioxide (TiO2) that Green People use is coated with a fine layer of silicates that shield the TiO2 from contact with oxygen and therefore prevent the formation of free-radicals.
As regards the issue of skin absorption, whilst the individual particles of TiO2 are small enough to be theoretically absorbed through the skin, when they are incorporated into a cream or lotion they form aggregations or clumps that that are too large to be absorbed beyond the stratum corneum, the outer horny layer of skin. This has been confirmed in a number of trials using human volunteers.
Based on this evidence, we feel that the use of ultra-fine TiO2 as a sunscreen is both safe and justified.