A new ice age is here. And it’s making amazing promises of pain-free joints and sculpted abs.

Cryotherapy — a freezing treatment turned piping-hot health trend — is being hyped by spas across the country, many of which sprang up within the last year.

Among them, NYC Cryo in Manhattan, promises that cryotherapy leads to “quicker surgical recovery time.” Thrive CryoStudio in Rockville, Maryland, claims it “alleviates symptoms from joint disorders, rheumatoid diseases, fibromyalgia, psoriasis and migraines.” Atlanta’s Cryo Elite Therapy said it “has been proven to improve peak levels of performance.” Omaha’s Ice Out CryoSpa boasts “alleviation of depression, anxiety, fatigue, insomnia.” CryoSF in San Francisco says the treatment “helps increase testosterone in men” and “reduce signs of aging, increases collagen production, improve skin condition and reduce cellulite.”

The problem: There’s no solid scientific evidence to back any of it. And the Federal Drug Administration is warning spas to stop making such claims.

Yet untold thousands are lining up every week to follow the likes of LeBron James, Tony Robbins and sundry celebrities and “Real Housewives” into cylindrical cryotherapy chambers, where they get blasted from the neck down with abominably cold air. (On Long Island, there are several cryotherapy salons, including Cryology in Babylon and KryoMed in Greenvale. Sessions run $25 to $90.)

What does cryotherapy do, exactly? Advocates like to say that the cold air forces blood to your core, tricking the body into thinking it’s experiencing hypothermia. From there, the claims get a bit fuzzy. Whole body cryotherapy believers say it acts as a supercharged ice bath, allowing muscles and tendons to more quickly recover from heavy training or pain, reducing inflammation. And many just claim, in the most unscientific of terms, that they feel energized by the treatment.

To find out what it feels like, I visited DistrictCryo, a new Washington, D.C., spa, for a three-minute session with air pouring in at minus 215 degrees Fahrenheit (mine was a “warmer” treatment; the air temperature can drop to minus 275 degrees). I wore socks, slippers and gloves that they gave me (men are also asked to keep their briefs on) and a robe, which I removed and handed over once I was entombed in the chamber. Moments in, there was a burning sensation on my forearms — minor perspiration turning to ice? — that disappeared within seconds. It felt unnaturally cold, as it should, since the air dropped well below earthly temperatures. (The lowest ever recorded at ground level is minus 128.6 degrees F.)

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My teeth chattered, I shivered; it was unpleasant but not intolerable. And afterward, I experienced a giddy surge of endorphins that lifted me for about an hour.

Following the oversize claims made by some cryotherapy providers — and after the death of one person in a cryotherapy chamber last year — the FDA issued a strongly worded warning against whole body cryotherapy in July. “Consumers may incorrectly believe that the FDA has cleared or approved whole body cryotherapy devices as safe and effective to treat medical conditions,” Aron Yustein, a medical officer in the FDA’s Center for Devices and Radiological Health, said in the FDA release. “That is not the case.”

The allure of cold therapies has been around for a long time. The Greeks promoted cold baths as a healthy tonic; the Romans celebrated in their frigidariums. Charles Darwin swore by a daily cold shower. But whole body cryotherapy was specifically developed in 1978 by a physician, Toshima Yamauchi, as an experimental way to treat rheumatoid arthritis. By the 1990s, it began to become popular in various European spas as an alternative treatment for chronic pain.

Cryotherapy spread to the celebrity set, with Jennifer Aniston, Daniel Craig and Jessica Alba reportedly booking appointments. Tony Robbins told fellow self-help and lifestyle guru Timothy Ferriss on his podcast that cryotherapy’s effects on him were “mind-boggling,” gave him “an explosion of endorphins” and said he’d purchased a unit for his home and for his mother-in-law, who suffered from arthritis.

All that Hollywood sizzle slowed last year after 24-year-old Chelsea Ake-Salvacion was found dead in a cryotherapy unit in the Las Vegas area spa where she worked. An autopsy later ruled that she had suffocated. She might have lost consciousness when she ducked her head down into the unit, possibly to retrieve her cellphone, and succumbed to the liquid-nitrogen-cooled air.

But if that tragedy cooled cryotherapy’s hype, it didn’t last.

One of the major U.S. distributors of cryotherapy units, Impact Cryotherapy, based in Atlanta, says sales have continued to soar. Impact announced in July it had sales of 200 units since the company launched in June 2014, but “we’ve probably bumped over 250 now,” he said this month. Another major distributor, CryoUSA, based in Dallas, lists more than 200 places it has sold cryotherapy units in the past five years.