Flying from coast to coast or overseas to exotic destinations may be thrilling, but flying the friendly skies for extended periods of time may lead to cancer. That’s according to a new study published in the journal Environmental Health.

Harvard researchers found that flight attendants report a higher incidence of non-melanoma skin cancer, uterine, gastrointestinal, cervical and thyroid cancers. They also found that female flight attendants with three or more children were more likely to be diagnosed with breast cancer, which was surprising because, typically, the more children a woman has, the lower her risk of breast cancer.

Moffitt researcher Dr. Shelley Tworoger says, “Flight attendants are exposed to a variety of occupational hazards that may impact health, including toxic fumes (e.g., exhaust), higher levels of cosmic radiation and circadian disruptions. However, the evidence that these individuals have a higher risk of cancer is mixed at best.”

The World Health Organization International Agency for Research on Cancer says ionizing radiation causes cancer and reproductive problems and they are currently looking at the effects of cosmic ionizing radiation.

Cosmic rays are radiation from the sun and outer space. Theses rays have existed since the beginning of time and their intensity hasn’t changed for millions of years. Passengers, as well as flight attendants, are exposed to cosmic ionizing radiation each time they fly. Why is that? Air gets thinner at higher altitudes. The farther you go from the Earth’s surface, the fewer the molecules to deflect incoming cosmic rays and with less atmospheric shielding there is more exposure to radiation. For a typical commercial airliner flying at 35,000 feet, the radiation exposure is 0.003 millisieverts (mSv) [2] per hour. It’s estimated that famed businessman Tom Stuker, who was portrayed by actor George Clooney in the movie Up in the Air, received the same amount of radiation logging more than 18 million miles as he would have if he received 1,000 chest x-rays.  You can calculate your in-flight cosmic radiation exposure here.

A more unpredictable form of cosmic radiation is the stream of particles the sun emits known as solar wind. Occasionally, the sun will release a burst of energy called a solar flare. Some of this radiation can enter the Earth’s atmosphere and contribute to in-flight radiation exposure. Though solar flares occur monthly, only about one per year impacts radiation levels at flight attitudes, which means while the average passenger probably isn’t affected, it may impact flight crews. The National Institute for Occupational Safety estimates that an average pilot will experience six solar flares in a typical 28-year career. It can be difficult to reduce your exposure to solar particle events because they can happen with little warning. You can find out whether a solar particle event is currently active here .

What can you do to reduce your exposure to cosmic radiation during your next flight? The Centers for Disease Control recommends:

• Reducing time spent on long flights, flights at high altitudes and flights that fly over the poles because these flight conditions are known to increase the amount of cosmic radiation exposure.
• If you are pregnant or planning a pregnancy, it is important to consider your work exposures, including cosmic radiation. If you are pregnant and aware of an ongoing solar particle event when you are scheduled to fly you may want to consider trip-trading or other rescheduling actions if possible.
  • For flight attendants, a NIOSH study found that exposure to 0.36 mSv or more of cosmic radiation in the first trimester may be linked to increased risk of miscarriage.
  • Also, although flying through a solar particle event doesn’t happen often, a NIOSH and NASA study found that a pregnant flight attendant who flies through a solar particle event can receive more radiation than is recommended during pregnancy by national and international agencies.

Dr. Tworoger says when considering your cancer risk from flying it’s important to keep in mind, “These studies are not adjusting for individual level factors; they are subject to ‘residual confounding.’ One of the papers found a higher risk of breast cancer in flight attendants than women in other jobs, but that was mostly because the flight attendants had fewer children and older age at first birth, both of which increase the risk for breast cancer.”

Plus, according to the Centers for Disease Control, whether you fly or not, a person’s average dose from cosmic radiation is 0.33 mSv (33 mrem) or 11 percent of our yearly exposure to all natural sources of radiation.