Knotted, I have that Neutrogena titaniumoxide-only sunblock lotion too. It's the one I switched to after the hives episode. It seems fine.
But i just got a tube of Dr. Hauschka's non-chemical sunblock SPF 15 (Tit.dioxide+zinc ox.). Very expensive, but I like the emollient qualities it has, and the smell is pleasing to me. (I had to get rid of some sunblocks I tried because even the "non-scented" ones had aromas I found unpleasant after a while. I have dry face skin and the Dr. H's seems to help that more than the Neutrogena which is "thinner".

I read somewhere that once you get to spf 15, adding higher spf numbers doesn't really multiply the effectiveness mathematically the way you think it does. Sort of like how 1% milk does not have half the fat of 2% milk, like you would expect it to.
Can't remember where I read about it though. Anyone else read that?
I do know that I've never noticed a protection difference between say a 20 and a 35 at all.