I think it is more what mannykannot said, combined with the fact that chlorine/salt/sand will also irritate skin, as well as the fact that sun reflecting off of water/glass/metal is not just reflecting visible light (sometime in the past few months there was a great thread on here with a guy talking about how they use mirrors to reflect sun onto solar panels where he works in Canada I think).

Snow sunburn is also a thing, IIRC snow can reflect as much as 90% of the UV. You can actually go 'snowblind' from this uv reflection.