Is flying bad for your health?
There has been some reports which have noted a higher than average incidence of certain cancers in aircrew. The reports are somewhat inconclusive


  Overall, the reports suggest that pilots are at increased risk of malignant melanoma, non-melanoma skin cancer, and possibly acute myeloid leukemia, and that cabin crew are at increased risk for breast cancer and malignant melanoma. However, the question remains as to whether the observed excesses are due to occupational exposures or non-occupational factors, such as reproductive history and lifestyle


Source: British Medical Journal

Research is ongoing.