Well, look at the air you are breathing...
I see to remember something about the radiation exposure, much less shielding and much more exposure from the suns harmful radiation?
For this reason, the Centers for Disease Control and Prevention (CDC) classifies airline crewmembers as radiation workers.
In fact, the National Council on Radiation Protection and Measurements reported in 2009 that aircrews have, on average, the highest yearly dose of radiation out of all radiation-exposed workers in the US.
http://www.businessinsider.com/airpl...titude-2015-11
Even the FAA is on it...
https://www.faa.gov/data_research/re.../radiobiology/
https://www.faa.gov/data_research/re...biology/cari7/