Let's talk Sunblock!

[OakLeaf]

Okay, I'm usually the one who sits here and tracks stuff down .... but I'm woozy from a late night concert.

Is there any scientific basis for defining nanoparticles as <100 nM? Or is that just an arbitrary cut-off? Because if it's just arbitrary, I'd like to see some research on titanium dioxide in the 100-200 nM range before I'd put that stuff on my skin.

Zinc oxide nanoparticles are thought to be safe, and IIRC, EWG actually expressed some surprise a year or two ago when it was found that zinc oxide nanoparticles are inert and do not penetrate the skin. Titanium dioxide nanoparticles, OTOH, are highly reactive to light. I'd want to know more about what happens with the slightly larger particles.