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DEET ate my backpack 4-Jan-2011 At 5:41:06 PM ET

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That's a link to a commentary and not a paper... nor was that section referenced... Though the author is affiliated with a reputable group (according to him anyway... a quick search through the University of New Mexico Cancer Center and Department of Internal Medicine's webpage doesn't list him in their personal...) what is written here is just one individual's opinion (as are all the posts in this forum including this one...)

I'm no expert in the field, however I do know that ZnO and TiO particles (the new controversial "nanoparticles" found in some sunscreens) have known effects when inhaled (a possibility if you do dry synthesis, e.g. thermal evaporation, laser ablation, arc discharges, etc) and precautions are usually made not to inhale the products. US OHS guidelines
http://www.osha.gov/SLTC/healthguidelines/zincoxide/recognition.html

As for absorption through the skin... according to the (very) brief summary provided by Therapeutic Goods Administration

The TGA review concluded that:
-The potential for titanium dioxide and zinc oxide nanoparticles in sunscreens to cause adverse effects depends primarily upon the ability of the nanoparticles to reach viable skin cells; and
-To date, the current weight of evidence suggests that titanium dioxide and zinc oxide nanoparticles do not reach viable skin cells; rather, they remain on the surface of the skin and in the outer layer of the skin that is composed of non-viable cells.
http://www.tga.gov.au/npmeds/sunscreen-zotd.htm

However if you read the detailed report on http://www.tga.gov.au/npmeds/sunscreen-zotd.pdf, reference 3 on page 5, reference 6 on page 7 and reference 40 on page 30 (and possibly more that I missed) provide suggest that the particles are absorbed by the skin cells.

At my workplace, the consensus is that there has not been enough studies (or time) in the area to make any conclusions and precautions are made so no skin contact or inhalation is made when producing these particles (better safe than sorry...).

In the end it's a choice of whether you want to get burnt and have an increased chance of getting melanoma, POSSIBLY getting some unknown disease LATER in life (most if not all Australian regulatory bodies have been satisfied with the lack of short term health effects to allow the sale of "nanoparticle" sunscreens) or simply just staying out of the sun (and have Vit D deficiency instead...)