Because astronauts work in space, they are affected by solar flares and other high-energy particles from the sun. Although working inside the ISS is safe, working in a spacesuit can place astronauts in harms way. It is believed that a trip to mars and back may be a highly risky journey leading to significant long-term risks for cancer in the returning travelers. Not just astronauts are affected.
Airline pilots and flight crews, as well as frequent fliers, receive increased doses of radiation from solar flares.