NESTLED between a nail parlour and a tanning salon on Wilshire Avenue in Santa Monica, an upscale part of Los Angeles, is a newer kind of spa. Opened last year, CryoZone invites customers to spend $75 for three minutes in a cryogenic chamber cooled to -110°C for fledgling freezers and -132°C for chilling connoisseurs. The treatment is meant to calm inflammation and soothe muscle soreness, but Angelenos swear by it to solve all sorts of ills, from tennis elbow to the urgent need to lose a bit of weight before a daughter’s wedding.

Invented in Japan in 1978 as a remedy for rheumatoid arthritis, cryotherapy is not new. But it was not until European rugby and football teams started freezing themselves in the past decade that it became more popular. America, which boasts at least 400 cryotherapy spas, is the first place to offer wide access to it. Impact Cryotherapy, a group that manufactures cryosaunas, claims to have units in 38 states running more than 10,000 sessions a week. California, unsurprisingly, is in the vanguard: there are around 60 below-freezing-cold vats in the state.

On a sunny weekday in March, CryoZone’s minimalist space is buzzing. A man dressed in surfing trunks, a T-shirt and flip-flops had come to recover from marathon training. A woman in all-black Spandex is there to zap her back pain. Customers at the spa are invited into one of the centre’s two treatment rooms and told to strip down to their skivvies. A towel is provided to swipe any excess moisture off the skin and fleecy gloves, socks and slippers are donned to protect the extremities. (A professional runner got frostbite in 2011 when he underwent cryotherapy in sweaty socks).

Next customers step into a round canister that looks like a galactic witch’s cauldron, frothing with liquid nitrogen vapour, and ring a bell to solicit assistance. The chamber’s platform has been adjusted to ensure that the customer’s head pokes out of the top. A young woman in Nevada died in 2015 after she attempted to administer cryotherapy to herself, got stuck and asphyxiated from the lack of oxygen in the chamber. The spa’s friendly business-development manager presses the timer and instructs his charge to rotate slowly as he makes small talk to speed the three minutes. It doesn’t work. As the skin’s temperature drops from 33.8°C to 1 °C, horribly intense tingling starts—not so much pins and needles as swords and daggers. After 180 seemingly interminable seconds, the machine mercifully beeps.

Scientific studies on whole body cryotherapy are inconclusive at best. The Food and Drug Administration calls it a “trend that lacks evidence, poses risks”. Health-conscious Americans seem unfazed. Perhaps its because they’ve seen athletes and celebrities like Shaquille O’Neal, Kobe Bryant and Demi Moore use it. Or maybe they trust their own personal reactions to cold treatment over science. The woman in black Spandex gushes: “My back pain used to be crippling. Now I can exercise again.”