According to the sunscreen industry, ultraviolet rays are able to burn our skin, cause melanomas, etc. even on cloudy days. But they would say that, wouldn’t they? Some say UVA rays cause aging, while UVB rays account for burning.
Q: So are both UVA and UVB rays out there, even on cloudy days? If so, why are folks in sunny climes tanner than people from cloudy places such as Seattle (even controlling for the amount of time spent outside)? Do clouds have any protective value?
Some web research yields variations on the corporate line, but maybe Coppertone is telling the truth. Of course, they also say sitting in the shade gives little protection, what with rays bouncing off the sand and the concrete.