The sun emits energy over a wide range of wavelengths, including ultraviolet radiation that we can't see or feel. UV radiation isn't a completely bad thing, because short exposures to it generate vitamin D in our bodies, but if we're out in the sunlight too much, it can cause sunburn and ailments such as cataracts, suppression of the immune system, skin cancer and premature aging of the skin. And that stuff still happens, even though we've got the planet's atmospheric ozone layer to filter out most of the UV that the sun gives off, before it reaches us [source: EPA].
If an astronaut's bare skin was exposed to unfiltered sunlight in space, though, he or she quickly would develop a very bad case of sunburn. That won't happen as long as the astronaut is wearing a spacesuit, though, because the only transparent part is the helmet visor, whose plastic is coated with several layers of filtering to provide protection against such radiation [source: NASA].