New research indicates that airline pilots and cabin crew are twice as likely to suffer from skin cancer because of regular exposure to harmful ultraviolet rays from the sun at high altitude.
Analysis of 19 studies which included more than 266,000 people found that incidence of melanoma was between 2.21 and 2.22 higher for pilots and 2.09 greater for flight attendants, or more than twice the rate of the general population.
The incidence rate was attributed to ultraviolet rays filtering into planes at high altitude through cockpit windscreens and windows on the fuselage, the study's author said.
Doctor Martina Sanlorenzo, from the University of California at San Francisco, said the study had "important implications for occupational health and protection of this population."
The study appeared in the Journal of the American Medical Association Dermatology.
Researchers reported that at 9,000 meters (30,000 feet) above sea level, the cruising altitude of most commercial jets, carcinogenic ultraviolet rays were twice as powerful.
The levels were even higher when planes fly over thick cloud layers, which reflect up to 85 percent of the harmful rays back towards a plane.
The research showed that while pilots and flight crew were known to be at risk from ionizing radiation, ultraviolet exposure was not a well-recognized occupational risk.
In 2014, some 76,000 cases of melanoma were diagnosed in the United States, with 9,710 expected to die from the condition.