I wonder if you could dive in any of the cooling shirts? I'm sure the Zoot sleeves are form-fitting and non-water-retaining enough to go underwater with. But they don't make a full-coverage shirt.

I've read enough about titanium dioxide nanoparticles that I'm not convinced that's safe. So, zinc oxide it is for me, and just put it on thinly enough that I'm not *too* blue. I still get plenty of sun protection from a thin layer.