I purchased (on the advice of the wise mners) Neutrogena sheer dry touch factor 45 sunblock.
I have to say though...it hasn't stopped my chest from reddening. My face is ok as always have foundation as extra protection and none of the rest of me really burns but my chest is horrible when it's red! I'd so much rather be white!
I'm not talking about sitting in the sun here either, just wandering around in general.
So, apart from a polo-neck, what else is going to help?