The growing industry of cryotherapy, which exposes the body to very cold temperatures, is coming under scrutiny in the United States after a woman "froze to death" at a Las Vegas spa.
Chelsea Ake-Salvacion died earlier this month at the Rejuvenice beauty salon, which offers the deep freeze therapy intended to reduce pain and boost muscle tissues and skin.
The 24-year-old woman is believed to have entered one of the spa's cold chambers after business hours to relieve some aches, and was discovered the next day by a co-worker.
Her uncle Albert Ake told local media that his niece's body was found "rock solid frozen" inside the chamber the size of a phone booth.
Police said there was nothing suspicious about her death and closed the case.
But Nevada authorities on Wednesday (local time) said they would investigate safety and other issues linked to cryotherapy, which is used by celebrities and star athletes but is not regulated by any one body.
"Based on developing information ... questions about public and workplace safety within this relatively new industry has lingered," said in a statement Steve George, administrator of the Nevada Division of Industrial Relations, which oversees job safety.
He added that the probe would help the state to update safety standards and practices as related to cryotherapy.
The two Rejuvenice locations in Las Vegas have meanwhile been shut down, not due to Ake-Salvacion's death but for failing to purchase proper insurance for employees.
Advocates say whole body cryotherapy, which exposes the body to temperatures that can reach minus 151C, is effective in reducing muscle soreness, stress, rheumatism and various skin conditions.
A three-minute session inside a chamber costs up to US$100. Users wear gloves and slippers to prevent frostbite and chilblains (pernio).
Star athletes, including basketball player LeBron James, have increasingly turned to whole body cryotherapy as an alternative to ice packs and cold water baths and centres have opened in New York, Los Angeles and elsewhere.
One spa in Los Angeles says on its website that professional athletes "have discovered whole body cryotherapy as a powerful treatment to decrease recovery time and increase athletic performance."
But many experts warn that the treatment has not been proven to be medically sound and are urging further research to determine the short- and long-term effects.
"While it may give you an adrenaline rush and a quick jolt, there is no evidence that it is beneficial for improved health or any purported claims as a rejuvenation or detox," Robert Glatter, an emergency physician at Lenox Hill Hospital in New York, told AFP.
Glatter also noted that the treatment has not been proven to reduce muscle damage after exercise and that people react differently to sub-zero temperatures and need to be monitored.