Exposure to more intense shale gas development correlates with a higher risk of asthma attacks among asthma patients, according to a new study of Pennsylvania’s Marcellus Shale, one of the nation’s largest and most active fracking regions.

The paper, published Monday in JAMA Internal Medicine, a publication of the American Medical Association, didn’t examine the exact cause of the trend. But lead author Sara Rasmussen, a Ph.D. candidate in environmental health sciences at Johns Hopkins Bloomberg School of Public Health, said air pollution and stress are both plausible explanations.

Natural gas development releases various air pollutants including particulate matter, volatile organic compounds and sulfur dioxide. The equipment also produces loud noises and bright lights, which can increase anxiety and sleeplessness. Years of research show that all these factors can exacerbate asthma.

The paper adds to the growing research linking the natural gas industry to various health impacts including birth defects, respiratory problems and skin rashes. Rasmussen and her six co-authors launched the study in 2012, about four years after the Marcellus Shale boom took off in Pennsylvania.

Nicole Deziel, an assistant professor of epidemiology at Yale School of Public Health who was not involved in the paper, praised the scientists’ rigorous research methods. It “represents an important advancement,” she said in an email. “More health studies like this are needed.”