Nevada is looking into whether cryotherapy is safe for the general public after the death of a Las Vegas spa worker found inside a phone booth-sized chamber chilled with liquid nitrogen, regulators said Monday.

The state said it was shifting its investigation beyond workplace safety and the equipment used in the treatments to the health concerns surrounding the technology itself. The new approach to the investigation could lead to regulations for the industry, said Steve George, state Division of Industrial Relations administrator.

The use of whole body cryotherapy has been growing across the country, notably by professional athletes to recover from competition or training, but the unproven treatments that involve subjecting the body to extreme subzero temperatures have been largely unregulated worldwide.

It's been touted as a treatment for pain and inflammation, increased blood flow, weight loss, better skin or even to ward off aging and depression. But the science and medical community have so far not embraced it, and the chambers are not approved for medical use by the Food and Drug Administration.

Few states have reported pushing for regulations, writing it off as "alternative treatment."

Joseph Costello, a researcher with the University of Portsmouth in southern England who studies cryotherapy, published a study weeks ago indicating that there was no solid science to back up the treatment's primary claim that brief exposures to temperatures as low as minus-300 degrees Fahrenheit could aid muscle soreness.

He also has pressed for more research and consistent guidelines for use, saying he believes hundreds of thousands of people have used cryotherapy across the world but that he didn't know of any regulations.

"Different companies, different countries are using different temperatures and different durations of exposure," Costello said.

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Popular in eastern Europe for years, cryotherapy only hit the U.S. market about two years ago, experts have said. But it wasn't quite mainstream when Chelsea Patricia Ake-Salvacion, 24, was found dead inside a whole-body chamber, leading to widespread scrutiny. She apparently was using the chamber on her own after-hours at the spa where she worked. The cause of her Oct. 20 death is pending toxicology reports.

It took the state more than a week to open an investigation because the industry is so new that no agency assumed responsibility for it.

The Division of Industrial Relations is expected to look at all three businesses selling the service in the state as part of its comprehensive review. Revealing how little cryotherapy is understood, the state said it would start its research from scratch, reading brochures and examining the equipment, among other things.

"At this point, the equipment doesn't seem to be the problem, but we are doing our due diligence," said George, who is head of the state's workplace safety division that also includes the Nevada Occupational Safety and Health Administration.

George said the wider investigation would aim for regulations, because the state has determined that no federal agency offers guidelines on cryotherapy use. State health officials could not immediately provide more information on what kind of rules could be considered.