Air crews have about twice the incidence of melanoma and a one third higher incidence of breast cancer than the average population. According to the WHO, air crews are exposed to more radiation than is the general public, but the level still is very low. Experts believe that if higher cancer development levels really are linked with air travel, they could be associated with disruption of circadian rhythms and production of melatonin. This antioxidant protects DNA by picking up radicals, but if less melatonin is available, there is a greater risk of damage to DNA.