Glass windows absorb UVA, which is known to cause skin cancer.
The glass does not absorb all UVB.
UVB has never been shown to cause skin cancer, there appears to be no statistically significant indications of that.
UVB is suspected of acelerating skin aging.
It is also suspected of causing fatigue and temporarily surpressing the imune system. I tend to buy into this based on my personal experiences.
As an experiement I started using UVB sunblock. I noticed a reduced incidence of common colds. I also have more energy at the end of the day..I'm usually more eager to hit the gym now. YMMV.
As for other types of cancer, my father and I are both experienced nuclear energy professionals, and my dad is a radiation effects expert. We ran the numbers, and the elevated cosmic and non-light solar radiation to which an average pilot is exposed can be expected to cause a BARELY measureable statistical increase on cancer death. It is a real increase, but very small compared to the average population. Low altitude, mid-latitude flights (ie domestic) are safer than high altitude, high latitude, long range flying (assuming the same number of flight hours). A pilot who tries to live healthy will still have much better odds than smokers or others with bad lifestyle factors.
So why do pilots have more skin cancer?
Rick's opinion: Pilots tend to be very active, often outdoor oriented people who have a lot of time off...skiing, biking, surfing, running, hunting, ranching, etc. I think we simply get more UVA exposure than the avergae person due to lifestyle, not occupation.
I bet if you tracked some of the younger guitar-hero regional pilots for forty years or so, you would note no elevated skin cancer risk, but an alarming increase in carpal-tunnel syndrome and obesity-related diseases
