(Reuters Health) - Whole-body cryotherapy - a trendy procedure that exposes the naked body to subzero temperatures - isn’t backed by evidence and can be risky, doctors say.

Spas and gyms advertise cryotherapy as a way to treat sore muscles, back pain, and skin problems. But a report in the Journal of the American Academy of Dermatology highlights a danger.

In the report, a 71-year-old man using whole-body cryotherapy was severely burned when a nozzle malfunctioned and sprayed liquid nitrogen directly on his back for less than a minute. He had stinging, pain and redness, which developed into blisters with a yellow pus.

“With the rise of cryotherapy facilities and the ease that consumers can be treated, it’s important to spread awareness of the harmful side effects,” said coauthor Dr. Jordan Wang of Thomas Jefferson University Hospital, where the patient was treated.

Cryotherapy chambers engulf the body from the neck down in a liquid nitrogen mist at temperatures between minus-150 to minus 220 degrees Fahrenheit (minus-100 to minus-140 Celsius) for several minutes. The head stays above the top of the chamber.

“Most consumers are unaware of the potential side effects and the lack of data behind how useful treatments are,” Wang told Reuters Health by email.

“Cryotherapy is increasing in popularity, but it’s not an FDA-approved treatment, and there’s not good regulation of the safety of these devices,” said Dr. Lisa Chipps, a dermatologist in Beverly Hills, California. Chipps, who wasn’t involved with this case, is president-elect of the American Board of Facial Cosmetic Surgery.

“When patients are undergoing non-FDA-approved treatments, they need to be aware of the potential risks of that device or service,” she told Reuters Health by phone.

Traditionally, dermatologists use cryotherapy to treat skin lesions such as viral warts, some skin cancers, and precancerous sun spots. Applied in very small areas by a trained physician, the liquid nitrogen freezes the skin and lesion.

Whole-body cryotherapy was originally given to patients with multiple sclerosis or rheumatoid arthritis for anti-inflammation effects. In recent years, it’s become popular for a wider audience. Proponents say the extreme cold helps muscle recovery after strenuous activity better than ice packs or cold water immersion.

However, the FDA hasn’t approved any cryotherapy chambers and warns about potential harmful effects including asphyxiation, frostbite, burns and eye injuries. A 2015 Cochrane review of previously published studies found insufficient evidence to support the benefits of muscle recovery for active young men, and no data exist for women or elite athletes.

“If the burn had happened on the patient’s face in this case, that would have been disfiguring,” said Dr. Anthony Rossi, a dermatological surgeon at Memorial Sloan-Kettering Cancer Center in New York City, who wasn’t involved with this case.

“Most of these cryotherapy chambers shield the fingers and toes, but what about his genitals or other areas?” Rossi told Reuters Health by phone. “People are going into this thinking they’ll receive a medical benefit, but it’s a cool trend that lacks evidence.”

SOURCE: bit.ly/2QhjiPF Journal of the American Academy of Dermatology, online December 4, 2018.