studies still cannot tell us the actual risk of using products containing these tiny particles.

You put these materials on your skin and they disappear,

Are they being absorbed through the skin?

tested the toxicity of a range of nanoparticles, including zinc oxide, to human immune cells over period of 24 hours.

zinc oxide particles were the most potent

But quite a high dose of zinc oxide nanoparticles were needed to cause a response in immune cells,

Studies have limits

Even after these studies are done, the results may not tell us the actual risk of using commercially available nano-sunscreens.

the formulation of a sunscreen itself may have unique effects.

"It's a catch 22 because producers are modifying these things to make them work better

commercial formulations are trade secret

find something untoward about this then this could cause our products to be taken off the market plus could destroy the industry full stop