
If there is life somewhere in the cosmos that can communicate with us, sprung up on a distant planet (which seems surprisingly unavoidable according to the Drake equation), it might look like this...
PS i have no idea what they are doing.

Just got back from the OuterBanks in North Carolina--basking in the sun and swimming through the choppy ocean water was rejuvinating. But, i have to admit, despite all my precautions--slathering 30spf suscreen regularly and donning a large brim hat--i still got sunburned. On the last day.
Two days later, my sunburn has healed, and i got a link on twitter about nanosunscreens--i remember hearing about them back in 2006 and wondering--is this just another consumer scare?
Evidently, to increase the spf power of titanium-dioxide based sunscreens (like the Bananaboat 30 that i used in NC) several manufacturers have engineered lotions that include nanoparticles of the titanium-dioxide molecules. The nanoparticles have more surface area to aborb UVA and UVB rays and thus are more efficient at sequestering them away from your skin.
But, because of their miniscule size, nanoparticles can get in places other additives cannot. The nanoparticles in titanium sunscreen may be able to sneak themselves into the pores in your skin and cause toxicity or cellular disfunction (aka a skin reaction.) Some (possibly half-baked) studies have concluded that the nanoparticles are not harmful enough to warrant ripping the product off shelves. Other people are still worrried they are. Since nanoparticles are not a new chemical, just an old chemical crushed into smaller bits, the FDA has not deemed the new sunscreens worth re-regulating.
It seems like to me that more thorough research needs to be done (though Greenpeace would argue otherwise, citing a 2004 recommendation by the British Royal Society. In 2006, they and other raging environmental groups set out to make an example of the sunscreen manufacturers and establish a precident that all consumer products containing nanoparticles be thoroughly examined and adequately regulated. They were thwarted and the FDA remains icy to this day.)
So, if you've had a skin reaction lately while using sunscreen, it could be nanoparticlate matter in your lotion....or it could be something else entirely. Don't get all paranoid.