A study by a group of researchers at the Harvard T.H. Chan School of Public Health found that flight attendants are at a higher risk of getting cancer than the general population.

The study, published in the journal Environmental Health today, used data from the Harvard Flight Attendant Health Study and found that the group had a higher incidence of every kind of cancer they looked at. Flight attendants’ risk of breast cancer, melanoma, and non-melanoma skin cancer was particularly elevated, but the researchers also found a higher prevalence of uterine, cervical, gastrointestinal, thyroid cancers in the group.

The study does not draw any conclusions about the cause of these higher rates of cancer, but suggests that flight attendants’ high exposure to cosmic ionizing radiation at flight altitude, Circadian rhythm disruption, and poor cabin air quality are likely contributing factors. In addition, flight attendants who worked before smoking on board was banned were exposed to high levels of second-hand smoke.

American flight attendants didn’t get Occupational Safety and Health Administration protection until 2014, and even now their protections are limited. For instance, there are no official limits to the amount of cosmic ionizing radiation flight crews can be exposed to and their exposure is not monitored. Cabin crew have the highest average annual effective dose of cosmic ionizing radiation of all U.S. radiation workers.