U.S. flight attendants experience higher rates of several types of cancer compared with the general public, according to a study that calls attention to the potential risks of their working environment.

The Harvard University study, described as one of the largest and most comprehensive on the subject to date, found that flight attendants had a higher prevalence of each of the seven broad cancer types examined, particularly breast cancer, melanoma and non-melanoma skin cancers among females.

The findings, published in the journal Environmental Health, are all the more striking because flight attendants typically show lower rates of obesity and smoking than the general public, the study’s authors said. As of 2016, U.S. airlines employed about 116,600 flight attendants, according to federal data.

Flight attendants “have a pretty unique mix of potential carcinogens they’re exposed to. It’s not widely known and it’s not regulated the way it could be,” said Irina Mordukhovich, a research fellow at the Harvard T.H. Chan School of Public Health and the study’s corresponding author.

Those carcinogens most notably include higher doses of cosmic radiation that flight crews are exposed to because of long hours spent working at high altitude, a situation that can be exacerbated on flights at high latitudes or over the Earth’s magnetic poles.

Air crews have the largest average annual effective dose of all radiation-exposed workers in the U.S., according to 2009 findings by the National Council on Radiation Protection and Measurements.

While European regulators require monitoring of air crews’ radiation exposure and changes to their work schedules if it exceeds certain thresholds, there are no such rules in the U.S.

Other potential risk factors include sleep-cycle disruption brought on by overnight flights and crossing time-zones, past exposure to secondhand smoke in the cabin and ongoing exposures to chemicals such as pesticides, which are used to sterilize cabins on some international flights.

Researchers conducted a survey of 5,366 U.S. flight attendants in 2014 and 2015. The sample group was more than 80 percent female