As more research is emerging on the potential health effects of fracking, a new study — perhaps the largest to date of its kind — has found that people living near natural gas wells may be at increased risk for adverse health impacts, including skin and respiratory conditions.

Published in the January issue of Environmental Health Perspectives, the study is based on the self-reported health symptoms of nearly 500 people in 180 households in Washington County, Pennsylvania, a community home to some of the most long-standing and intense natural gas drilling activities. Researchers found that even when accounting for confounding variables, such as age, cigarette smoking, education level and occupation, residents who lived less than a kilometer away from a gas well reported more health symptoms than those living more than two kilometers away from a gas well. Peter Rabinowitz, a co-author of the study and an associate professor in the Environmental and Occupational Health Sciences Department at the University of Washington, said that to his knowledge, the study is the largest to examine general health conditions among people living near fracking sites.

“This doesn’t prove association,” Rabinowitz told me. “But we feel that it really adds significant evidence to questions of whether to keep looking at and taking seriously the potential for health effects (associated with fracking).”

To conduct the study, researchers used mapping technology to randomly select households that depend on naturally occurring water supplies — known in the study as ground-fed wells — which are vulnerable to fracking-related contamination. They literally went door to door, asking residents to participate in a general health study on residents’ health status. In fact, Rabinowitz said researchers purposefully did not describe it as a fracking study to help reduce any bias in participants’ responses. Rabinowitz added that compared to similar studies, this study went to great lengths to systematically eliminate selection bias — “we were open to seeing whatever the results may be,” he said. After gathering residents’ responses, researchers then mapped the distance of participating households to the nearest natural gas well. Here’s what they found.

The average number of reported health symptoms was greater among households located less than a kilometer from a gas well than in households more than two kilometers from a well. Residents living less than a kilometer from a gas well were also more likely to report skin conditions during the past year as well as upper respiratory symptoms. Even after adjusting for other health risk factors, such as smoking, household proximity to natural gas wells was still associated with increased health symptoms. The study did not find an association between proximity to a natural gas well and increased cardiac, neurological or gastrointestinal symptoms.

While the study did not undercover the exact causes of residents’ health symptoms, researchers hypothesized a number of possible contributors, such as exposure to certain chemicals via contaminated ground water, fracking-related air pollutants, and increased stress and anxiety associated with living closer to a gas well. Study authors Rabinowitz, Ilya Slizovskiy, Vanessa Lamers, Sally Trufan, Theodore Holford, James Dziura, Peter Peduzzi, Michael Kane, John Reif, Theresa Weiss and Meredith Stowe write:

Since most of the gas wells in the study area had been drilled in the past 5–6 years, one would not yet expect to see associations with diseases with long latency, such as cancer. Furthermore, if some of the impact of natural gas extraction on ground water happens over a number of years, this initial survey could have failed to detect health consequences of delayed contamination. However, if the finding of skin and respiratory conditions near gas wells indicates significant exposure to either fracking fluids and chemicals or airborne contaminants from natural gas wells, studies looking at such long-term health effects in chronically exposed populations would be indicated.

Rabinowitz told me that he was prepared to find no association between gas well proximity and health symptoms and was “somewhat surprised” at the results.

“It was very hard with previous studies to know how much was reporting bias versus a real effect,” he said. “We were prepared to see that as we controlled for bias, the effects would lessen.”

But that didn’t happen, and Rabinowitz said this most recent study underscores the need for ongoing health monitoring of those living near natural gas extraction activities to better understand potential health risks. In particular, he noted that greater study and surveillance of natural gas extraction workers would likely provide the most telling insights.

Overall, Rabinowitz told me that fracking-related health research is still very much in its infancy, though enough is known to justify precautionary steps. He noted that New York’s recent decision to move forward with a fracking ban, in which potential health risks were cited as a main justification, could help drive additional research efforts and highlight the importance of including public health experts in related policy discussions.

“We’re at a stage in which we know enough to recommend prudent precaution and exposure reduction,” he said. “We have a long way to go in terms of definitive studies and effective surveillance. We still don’t know what exposures are of greatest interest and how to best control and monitor those exposures.”

Rabinowitz noted that researchers followed the study’s participating households for two years — from 2012 to 2014 — and are in the midst of conducting a longitudinal assessment of potential health impacts. In addition, researchers are now analyzing data on agricultural and domestic animals living near fracking sites, as animals often serve as sentinels for environmental health hazards.

“When a significant new technology comes to an area, the public health impact needs to be considered,” he said. “In general, there’s always some trade-off between health impact and the introduction of a new technology and it’s important to know what that trade-off is going to be and how to manage it appropriately.”

To read a full copy of the new fracking study, visit Environmental Health Perspectives.

Kim Krisberg is a freelance public health writer living in Austin, Texas, and has been writing about public health for more than a decade.