Pilots and cabin crew members may be among the occupational groups facing the highest risk of death from cancers associated with exposure to ionizing radiation, according to a new US study published on August 17 in JAMA Internal Medicine. The findings have once again brought attention to the long-term exposure of flight crews to cosmic radiation, a natural form of ionizing radiation to which all passengers are exposed during flight, but which crews accumulate in significantly higher doses over the course of their careers.

The research, conducted by Vishal R. Patel, Michael Liu and Anupam B. Jena of Harvard Medical School and affiliated institutions, analyzed approximately 12.7 million deaths in the United States between 2020 and 2024. A total of 503 occupations were examined, including more than 14,000 pilots and over 7,000 cabin crew members. The data came from the US National Vital Statistics System, which includes information recorded on death certificates.

The researchers examined mortality from a group of cancers known to be associated with ionizing radiation. These included breast cancer, cancers of the central nervous system, multiple myeloma, certain types of leukemia and lymphoma, thyroid and prostate cancer, as well as melanoma and other skin cancers. Lung cancer was excluded from the analysis in order to reduce the influence of smoking as an important additional risk factor.

The results showed that cabin crew members had approximately 50 percent higher adjusted odds of dying from cancers in this group than the general working population, while pilots had approximately 36 percent higher odds. Among all occupations analyzed, cabin crew and pilots ranked at the top in terms of the adjusted proportion of deaths from these cancers, ahead even of occupations that work directly with radioactive sources, such as nuclear medicine technologists.

Cancers classified by the study as radiation-related accounted for approximately 6.9 percent of all deaths among cabin crew members and 6.7 percent among pilots. In the general working population, the figure was around five percent.

It is important to emphasize, however, that this does not mean cosmic radiation has been proven to have caused 6.9 or 6.7 percent of all deaths in these occupations. The study compared mortality patterns involving types of cancer that scientific literature has linked to ionizing radiation.

The study shows an association, but cannot prove causation

The findings are significant, but the study also has important limitations. The researchers did not have individual data on how many hours each pilot or cabin crew member had spent in the air, which routes they had flown, at what altitudes they had operated or what cumulative radiation dose they had received during their careers.

Death certificate data may also contain incorrectly recorded occupations, while the researchers could not fully separate the effects of radiation from other characteristics of work in commercial aviation. These include night work, frequent time-zone changes and long-term disruption of circadian rhythms. Pilots may also receive additional exposure to UV-A radiation through cockpit windows.

In a commentary published alongside the study in JAMA Internal Medicine, Australian radiation-health researchers Catherine Olsen and Ken Karipidis highlighted this combination of factors. At the same time, they noted that pilots and cabin crew did not show a comparable increase in mortality from cancers not associated with radiation, lending further support to the hypothesis that occupational exposure may play an important role, although it does not prove radiation to be the sole cause.

What exactly is cosmic radiation?

Cosmic radiation is a natural part of the environment. Earth is constantly being struck by extremely high-energy particles from space. Some originate from the Sun, while galactic cosmic radiation comes from outside the Solar System and is associated with high-energy processes in space, including supernova explosions.

At ground level, we are protected from most of this radiation by the atmosphere and Earth’s magnetic field. An aircraft flying at an altitude of 10 or 12 kilometers, however, is above a large proportion of the atmosphere, meaning that this protective layer is much thinner.

When primary high-energy cosmic particles collide with molecules and atomic nuclei in the atmosphere, they create a cascade of secondary particles. According to the International Atomic Energy Agency, or IAEA, the radiation field at typical commercial aviation altitudes consists of neutrons, protons, electrons, positrons and photons. Depending on altitude, geographic latitude and the solar cycle, neutrons can account for approximately 40 to 80 percent of the effective radiation dose.

The term “cosmic radiation” therefore does not describe a single type of ray, but rather a complex mixture of high-energy particles and electromagnetic radiation.

Is this the same as X-rays?

Not in the conventional sense. X-rays are one form of electromagnetic ionizing radiation, similar to gamma rays. They have no electrical charge and consist of photons with enough energy to ionize matter, meaning they can remove electrons from atoms.

In medicine, X-rays are usually produced in an X-ray tube by accelerating electrons and then rapidly decelerating them against a target.

Collisions involving cosmic particles in the atmosphere can also produce high-energy photons, but the radiation to which flight crews are exposed cannot simply be described as “X-rays from space.” At commercial aviation altitudes, a significant and often dominant proportion of the biologically relevant dose comes from neutrons and other secondary particles.

This is also why conventional lead shielding, such as that used in medical X-ray environments, is not a practical solution for commercial aircraft. The amount of shielding material required would add substantial weight, while protecting against high-energy neutrons is considerably more complicated than shielding against conventional medical X-rays.

How does ionizing radiation affect the human body?

The term “ionizing” means that the radiation carries enough energy to alter the electronic structure of atoms and molecules through which it passes. In the human body, it can damage molecules directly or indirectly damage DNA through the production of free radicals.

Cells successfully repair much of this damage. Problems arise when repairs are incomplete or incorrect. In rare cases, these changes can produce mutations that contribute to the development of cancer years or even decades later.

At the radiation doses encountered by airline passengers and flight crews, acute effects such as radiation sickness are not expected. These are much lower doses, where the primary concern is a very small individual risk that increases with cumulative exposure.

This is why there is an important distinction between a passenger who flies several times a year and a crew member who may spend tens of thousands of hours at cruising altitude over the course of a career.

How much radiation does a passenger receive on a flight?

The dose depends on the duration of the flight, altitude, geographic latitude, route and solar activity. In general, radiation exposure increases with altitude and at higher latitudes because atmospheric shielding is reduced and the protective effect of Earth’s magnetic field is weaker.

The US Centers for Disease Control and Prevention, or CDC, states that a passenger on a single flight between the east and west coasts of the United States receives approximately 0.035 millisieverts, or mSv, of cosmic radiation. The CDC also notes that two such transcontinental flights result in a dose roughly comparable to one chest X-ray. For an occasional passenger, such exposure levels are considered very low.

For comparison, RadiologyInfo, operated jointly by the American College of Radiology and the Radiological Society of North America, estimates the effective dose from a conventional chest X-ray at approximately 0.1 mSv. A dental X-ray is around 0.005 mSv, while a chest CT scan can result in a dose of approximately 6.1 mSv.

The United Nations Scientific Committee on the Effects of Atomic Radiation, or UNSCEAR, has previously estimated doses for various routes departing Frankfurt. The figures ranged from approximately 3 to 6 microsieverts for a flight to Rome, 32 to 75 microsieverts to New York, 45 to 110 microsieverts to San Francisco and 28 to 50 microsieverts to Singapore. One millisievert equals 1,000 microsieverts.

The ranges vary because of differences in altitude, routing and solar activity.

In other words, there is no particular reason for concern for an occasional passenger taking several flights a year. The situation is considerably different for someone who spends 600, 800 or more hours every year at cruising altitudes.

Flight crews can receive several millisieverts per year

The IAEA states that at altitudes of approximately 9,000 to 12,000 meters and at geographic latitudes typical of routes between northern Europe and North America, effective dose rates generally range from around 4 to 8 microsieverts per hour. As a practical average, it cites approximately 4 µSv/h for long-haul flights and around 3 µSv/h for shorter flights. Typical annual flight time for crew members ranges between 600 and 900 hours.

UNSCEAR has estimated that crew members operating shorter routes typically receive around 1 to 2 mSv per year, while long-haul crews commonly accumulate approximately 3 to 5 mSv annually.

This places flight crews among occupational groups with the highest average exposure to ionizing radiation. The JAMA study itself also notes that US aircrew have the highest average annual effective dose of ionizing radiation among the occupational groups examined.

Polar routes are particularly relevant. Earth’s magnetic field provides its strongest protection closer to the equator, while its shielding effect becomes weaker toward the poles. For that reason, the FAA takes into account not only altitude and flight duration when calculating radiation doses, but also geographic position, solar activity and geomagnetic conditions.

The agency developed its CARI-7 computer model specifically to estimate the effective radiation dose received by an individual during a particular flight.

Solar storms can temporarily increase radiation exposure

In addition to the relatively constant background of galactic cosmic radiation, there are occasional events associated with the Sun. During powerful solar particle events, the number of high-energy particles reaching Earth can increase sharply.

Such events are uncommon, but they are particularly relevant for polar operations and pregnant crew members.

The US National Institute for Occupational Safety and Health, or NIOSH, notes that a cabin crew member flying through a major solar particle event during pregnancy could, under certain circumstances, receive a radiation dose exceeding values recommended by national and international bodies for pregnancy.

NIOSH also cites research that identified an association between exposure of at least 0.36 mSv during the first trimester and an increased risk of miscarriage among cabin crew, while emphasizing that this represents an epidemiological association that requires further research.

Europe and the United States take different approaches

The issue is particularly relevant in the United States because, although the FAA has recognized cosmic radiation as an occupational exposure for flight crews for decades, there is no comparable mandatory federal system for monitoring individual crew doses such as those used in several other radiation-exposed industries.

In June 2026, the US National Academies of Sciences, Engineering, and Medicine published a report commissioned by Congress that concluded existing US approaches to monitoring crew exposure and communicating the associated risks were “inconsistent and insufficient.”

The Academies recommended that the FAA treat cosmic radiation more formally as an occupational hazard, introduce more systematic tracking of individual doses and require airlines to establish radiation-protection programs.

European regulations already go further.

Council Directive 2013/59/Euratom requires employers to assess exposure when the effective dose received by aircrew is liable to exceed 1 mSv per year, inform workers about the health risks involved and take exposure into account when organizing work schedules in order to reduce the doses received by highly exposed crew members.

Special provisions also apply to pregnant crew members, while additional requirements apply where annual doses may exceed 6 mSv.

South Korea has already recognized a crew member’s death as occupationally linked to cosmic radiation

The issue has also moved beyond statistical research.

In 2023, South Korea’s Korea Workers’ Compensation and Welfare Service recognized the cancer death of a 53-year-old Korean Air cabin crew member as being occupationally associated with long-term exposure to cosmic radiation.

According to reports at the time from AeroTime and South Korean media, the crew member had worked for approximately 25 years and had averaged more than 1,000 flight hours annually. Around half of his working time involved long-haul services to Europe and North America, including routes over high geographic latitudes.

Such an administrative or legal decision is not, by itself, scientific proof that radiation was the sole cause of the disease, but it does demonstrate that cumulative occupational exposure among flight crews is increasingly being taken seriously.

The risk remains very low for passengers, while cumulative exposure matters for crews

The new study therefore does not mean that air travel itself is dangerous or that taking several flights per year will significantly increase a passenger’s risk of developing cancer.

The CDC explicitly states that radiation doses associated with ordinary air travel are low and that no measurable health effects are expected for occasional travelers.

For pilots and cabin crew, however, the issue is different. Decades spent working at altitudes of around ten kilometers can mean thousands of flights and cumulative radiation doses measured in tens of millisieverts over the course of a career.

The latest results therefore do not provide definitive proof that cosmic radiation causes higher cancer mortality among flight crews, but they add weight to arguments in favor of systematic exposure monitoring, improved crew education and further long-term research.

As the US National Academies concluded just two months before the publication of the latest study, the dose received on an individual flight is small. When assessing occupational exposure, however, the important factor is what accumulates over an entire flying career.

Sources:

• JAMA Internal Medicine – “Cancer-Related Mortality Among US Pilots and Flight Attendants” and the accompanying commentary by Catherine Olsen and Ken Karipidis
• Harvard Medical School and Associated Press – additional information on the study methodology and findings
• CDC/NIOSH – cosmic radiation, passenger exposure and occupational health risks for aircrew
• International Atomic Energy Agency (IAEA) and UNSCEAR – composition of cosmic radiation and typical doses at commercial aviation altitudes
• National Academies of Sciences, Engineering, and Medicine – June 2026 report on occupational radiation exposure among flight crews
• Federal Aviation Administration – CARI-7 model for estimating cosmic-radiation exposure during flight
• EUR-Lex – Council Directive 2013/59/Euratom on protection of aircrew from cosmic radiation
• RadiologyInfo – comparative doses from medical X-ray and CT imaging
• AeroTime and South Korean media – the Korean Air occupational disease case