AVELLA, Pa. — About two years ago, Dr. Amy Pare began treating members of the Moten family and their neighbors from a working-class neighborhood less than half a mile from a natural gas well here.

A plastic surgeon whose specialty includes skin cancer, Pare removed and biopsied quarter-size skin lesions from Jeannie Moten, 53, and her niece, only to find that the sores recurred. “The good news is that it wasn’t cancer, and the bad news is that we have no idea what it is,” Pare said.

Determined to understand the illnesses, Pare went last May to the Motens’ neighborhood to collect urine samples from a dozen people. To her dismay, she found chemicals not normally present in the human body: hippuric acid, phenol, mandelic acid.

The Motens and their neighbors suspect their ailments could be tied to the natural gas well. Pare says she is not sure what is causing their problems. But she worries that she may have a hard time determining the exact cause because of a provision in a new Pennsylvania law regulating natural gas production.

The law compels natural gas companies to give inquiring health care professionals information about the chemicals used in their drilling and production processes — but only after the doctors or nurses sign a confidentiality agreement.

Some physicians complain that the law is vague and lacks specific guidelines about how they can use and share the information with patients, colleagues and public health officials, putting them at risk of violating the measure. But refusing to sign the confidentiality agreement denies them access to information that could help treat patients.

“I just want to make my patients healthy,” Pare said, adding that she might sign an agreement. “And I can’t do that if I don’t know what it is that’s making them sick.”

The possibility that increased natural gas development could threaten public heath lies at the core of resistance to a controversial process known as hydraulic fracturing, or fracking. The technique involves high-pressure injection of water and sand laced with chemicals deep underground to break shale formations and unlock oil and gas deposits.

Some people living near well sites have complained that their well water has been contaminated by fracking. The industry asserts that tiny amounts of chemicals are used in fracking and that the water problems are unrelated to the procedure.

Supporters of the Pennsylvania law — including the gas industry, Republican Gov. Tom Corbett and many legislators — said it was designed to help health care providers. Environmental groups and opposing lawmakers said the provision was not in the natural gas law’s original version and was slipped in behind closed doors at the last minute by industry-friendly legislators.

Patrick Henderson, the governor’s energy executive, said the new law would increase disclosure. Companies would have to share the chemical composition of fluids they use in natural gas production, including proprietary mixes. The confidentiality agreement would not prevent doctors from sharing information with colleagues or patients, only with the company’s competitors, he said.

Dr. Marilyn Heine, president of the Pennsylvania Medical Society, said her group had been assured by the state that as regulations are developed to implement the law, state officials “will clarify the provisions so that physicians will know what they can do.”

Some doctors, however, want the details in writing before they sign any confidentiality agreements.

“Right now, any physician reading the law would not go anywhere near the issue, because the language of the law has a very chilling effect,” said Dr. Bernard Goldstein, former dean of the University of Pittsburgh Graduate School of Public Health and an expert on possible health effects of natural gas development. “I very much hope that the regulations permit” information sharing, he added.

So far, there are no comprehensive, independent studies of the possible health effects of natural gas development.

Dr. Sean Porbin, a family practitioner in Avella, thinks natural gas development could revive many struggling towns in Pennsylvania. “We need to ask questions,” he said. “It’s not about shutting down industry, but fixing it. And if the data show what they’re doing is safe, then we need to defend them.”

Pennsylvania’s new law is not unprecedented, according to the state’s Republican leadership, the natural gas industry and at least two prominent environmental groups. The measure is based on a new rule in Colorado and on two decades-old federal laws from the Environmental Protection Agency and the Occupational Health and Safety Administration.

The comparisons between Pennsylvania’s provision and the federal laws, however, are inexact, experts said. According to a statement from OSHA, what doctors can disclose and to whom would come down to “the terms of the agreement between the employer and the health care provider.”

In any case, there is little precedent for how nondisclosure agreements between doctors and companies would work when the patients are residents near a fracking site, not company employees, experts said.

If the state guidelines are stringent, doctors probably will forgo the agreement — and the information they are seeking from a company, Goldstein and other physicians said. That, too, could imperil doctors.

“It exposes us to lawsuits from our own patients, who might say, ’Why didn’t you sign the confidentiality agreement?’ or if you did, ’Why didn’t you share the information with so-and-so?’ ” said Dr. Mehernosh Khan, who has filed suit against the state over the provision. “The law sets up a precedent for doctors not being able to practice medicine properly.”