(sorry, link directly to article does not work) relevant piece below
The concentration of ultraviolet (UV) rays -- the ones that can cause sunburn, skin cancer, and other problems -- is greater at altitude than on the ground. The higher up you go, the less of the Earth's atmosphere you have between you and the sun. The atmosphere normally acts to filter out some of the sun's rays before they reach the ground.
Pilots are exposed to substantial doses of UV rays through the flight deck windscreen while flying. This can lead to skin damage of several varieties, ranging from premature aging and wrinkles to skin cancer.
UV rays also can do serious damage to the damage the eyes, causing cataracts, a disorder that clouds the lens of the eye and may ultimately result in partial or full blindness. UV exposure also can cause inflammation of the corneas, the irises, and the membranes that line the eyelids.
UV radiation is not warm!
There are debates as to the amount of UV experienced by flight crews, but a basic risk assessment goes like this:- UV is not good and can produce devastating sight problems. To control this risk is so easy and cheap, you'd be foolish not to.
http://www.faa.gov/pilots/safety/pil...sunglasses.pdf
WP
Ag bi has deleted sarcastic reference to UV from cathode ray tubes, probably because he's found out that CRT do produce some UV radiation!