This higher risk may be due to the increased exposure to ionizing radiation and ultraviolet (UV) radiation at higher altitudes, the researchers said.

"At 9,000 metres, where most commercial aircraft fly, the UV level is approximately twice that at the ground," said study author Martina Sanlorenzo from the University of California, San Francisco.

The researchers assessed the risk of melanoma in pilots and airline crew by reviewing medical literature. Their meta-analysis included 19 studies with more than 266,000 participants.

The overall standardized incidence ratio (SIR) of Melanoma for any flight-based occupation was 2.21, the summary SIR for pilots was 2.22 and for cabin crew 2.09.

The study appeared online in the journal JAMA Dermatology.

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