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Being a flight attendant has its bonuses, like getting to travel the world for free, meet new people, and earn well above the average American salary. But it’s not all free snacks and flights to Paris. The job comes with some costs too—like erratic schedules, aggressive passengers, and significant delays.

But those, while frustrating, may be the tip of the iceberg. This week, new research is boosting concerns about an even more severe hazard: the increased risk of cancer. The study, published in the journal Environmental Science, is the second wave of a 2007 Harvard Flight Attendant Health Survey aimed at analyzing how “occupational exposures impact the health of flight attendants.”

The initial 2007 study analyzed the general health of flight attendants, finding elevated rates of things like sleep disorders, fatigue, and depression. For this new study, the researchers from the Harvard T.H. Chan School of Public Health focused on cancer, recruiting more than 5,000 current and former flight attendants— 80 percent of whom were female—to share their history.

Once cataloged, the stats were compared with the National Health and Nutrition Examination Survey (NHANES), a nationwide study from the Centers for Disease Control and Prevention. The conclusion is stark. Flight attendants show a higher prevalence of every cancer studied, including breast, uterine, gastrointestinal, thyroid, cervical, melanoma and non-melanoma skin cancer.

Although the authors were not able to nail down an exact reason, concerns have been building for years about the exposure to cancer-causing agents (called carcinogens) on airlines. In this case, the two significant identified risks—which may be driving these numbers—are disrupted circadian rhythms and what’s called “cosmic ionizing radiation.”

Cosmic ionizing radiation is radiation that comes from outer space and is caused by things like solar flares. While only a small amount of it reaches earth, it’s present in much higher doses at flight altitudes. According to the CDC, flight attendants and pilots are exposed to it on every single flight, exposing them to the largest annual ionizing radiation dose of all U.S. workers.

For years, the World Health Association (WHO) has declared a direct link between long-term exposure of this cosmic ionizing radiation and cancer. As a result, the European Union has placed limits on the amount of radiation exposure for flight crew members, specifically for pregnant women, to lessen the risk of cancer and other health effects. Although the CDC offers warnings about the dangers, it doesn’t suggest that the ionizing radiation levels are actively monitored for U.S. flight crews.

On top of that potential carcinogens, the Harvard researchers also point out pervasive disruption of sleep circadian rhythms among flight attendants, due to things like night shifts and changing time zones. While changing sleep cycles may seem benign, a chronically disrupted sleep cycle has been linked to multiple types of cancer including skin and breast.

In the wake of the study, former flight attendants have taken to Twitter to express their concern about how long the information has been concealed.

Echoing their thoughts is Harvard epidemiologist Irina Mordukhovich, one of the researchers involved. “Our study informs future research priorities regarding the health of this understudied group of workers, who have a wide range of job-related exposures to known and probable carcinogens,” she said in a statement. “Our findings raise the question of what can be done to minimize the adverse exposures and cancers common among cabin crew.”