Risk Factors
UV Radiation
These studies suggest flight duties increase the risk for cutaneous malignancy. UV radiation is a known risk factor for skin cancer.12 The main body of the aircraft may protect the cabin’s crew and passengers from UVR, but pilots are exposed to more UVR, especially in aircraft with larger windshields. A government study in 2007 examined the transmittance of UVR through windscreens of 8 aircraft: 3 commercial jets, 2 commercial propeller planes, 1 private jet, and 2 small propeller planes.13 UVB was attenuated by all the windscreens (<1% transmittance), but 43% to 54% of UVA was transmitted, with plastic windshields attenuating more than glass. Sanlorenzo et al14 measured UVA irradiance at the pilot’s seat of a turboprop aircraft at 30,000-ft altitude. They compared this exposure to a UVA tanning bed and estimated that 57 minutes of flight at 30,000-ft altitude was equivalent to 20 minutes inside a UVA tanning booth, a startling finding.14
Cosmic Radiation
Cosmic radiation consists of neutrons and gamma rays that originate outside Earth’s atmosphere. Pilots are exposed to higher doses of cosmic radiation than nonpilots, but the health effects are difficult to study. Boice et al15 described how factors such as altitude, latitude, and flight time determine pilots’ cumulative exposure. With longer flight times at higher altitudes, a pilot’s exposure to cosmic radiation is increasing over the years.15 A 2012 review found that aircrews have low-level cosmic radiation exposure. Despite increases in MM and NMSC in pilots and increased rates of breast cancer in female aircrew, overall cancer-related mortality was lower in flying versus nonflying controls.16 Thus, cosmic radiation may not be as onerous of an occupational hazard for pilots as has been postulated.
Altered Circadian Rhythms
Aviation duties, especially in the military, require irregular work schedules that repeatedly interfere with normal sleep-wake cycles, disrupt circadian rhythms, and lead to reduced melatonin levels.8 Evidence suggests that low levels of melatonin could increase the risk for breast and prostate cancer—both cancers that occur more frequently in female aircrew and male pilots, respectively—by reducing melatonin’s natural protective role in such malignancies.17,18 A World Health Organization working group categorized shift work as “probably carcinogenic” and cited alterations of melatonin levels, changes in other circadian rhythm–related gene pathways, and relative immunosuppression as likely causative factors.19 In a 2011 study, exposing mice to UVR during times when nucleotide excision repair mechanisms were at their lowest activity caused an increased rate of skin cancers.20 A 2014 review discussed how epidemiological studies of shift workers such as nurses, firefighters, pilots, and flight crews found contradictory data, but molecular studies show that circadian rhythm–linked repair and tumorigenesis mechanisms are altered by aberrations in the normal sleep-wake cycle.21
Cockpit Instrumentation
Electromagnetic energy from the flight instruments in the cockpit also could influence malignancy risk. Nicholas et al22 found magnetic field measurements within the cockpit to be 2 to 10 times that experienced within the home or office. However, no studies examining the health effects of cockpit flight instruments and magnetic fields were found.
Final Thoughts
It is important to counsel pilots on the generally recognized, nonaviation-specific risk factors of family history, skin type, and UVR exposure in the development of skin cancer. Additionally, it is important to explain the possible role of exposure to UVR at higher altitudes, cosmic radiation, and electromagnetic energy from cockpit instruments, as well as altered sleep-wake cycles. A pilot’s risk for MM may be twice that of matched controls, and the risk for NMSC could be higher.8,11 Although the literature lacks specific recommendations for pilots, it is reasonable to screen pilots once per year to better assess their individual risk and encourage diligent use of sunscreen and sun-protective measures when flying. It also may be important to advocate for the development of engineering controls that decrease UVR transmittance through windscreens, particularly for aircraft flying at higher altitudes for longer flights. More research is needed to determine if changes in circadian rhythm and decreases in melatonin increase skin cancer risk, which could impact how pilots’ schedules are managed. Together, we can ensure adequate surveillance, diagnosis, and treatment in this at-risk population.
