In the early days of the pandemic, the celebrity trainer and nutritionist Harley Pasternak bought a chest freezer for his backyard. At the time, Mr. Pasternak, 48, who works with Ariana Grande, Maude Apatow and H.E.R., thought he might need it to store extra food. But when the grocery stores in West Hollywood stayed open, he converted the freezer into a makeshift cold plunge: a tank of icy cold water that he could dip into for a few minutes a day to ease his back pain and anxiety.

“It’s horrible for the first sort of 30 seconds to a minute,” he said of the ice-bath experience. “But when you get past that, you kind of feel this sense of Zen, and this calm, and then when you get out, you feel this burst of energy and positivity.”

Cold-plunge devotees say the practice offers all kinds of benefits, including mental clarity, pain management and even weight loss, citing proponents like the Dutch motivational speaker Wim Hof and the Stanford neuroscientist Andrew Huberman.

There are few scientific studies on the practice, but Tracy Zaslow, a 48-year-old sports medicine doctor at Cedars Sinai in Los Angeles, said there is data that suggests cold exposure can at least help with muscle soreness. The science on whether regular cold plunges can help with anxiety and weight loss is less clear.

Regardless of the benefits, the practice has become popular enough that manufacturers are now swooping in to make it easier for celebrities and other wellness seekers to get their perfectly freezing ice baths on demand.

Mr. Pasternak discovered this when he went searching for an alternative to his chest freezer, which turned out not to be the ideal vessel for the practice. The water inside did not circulate, which meant that after a minute or two, Mr. Pasternak’s body heat would warm it up, rendering the exercise somewhat less effective. Keeping it clean was also a pain. “I remember buying on Amazon some fish tank filter thing,” he said.

Luckily, Mr. Pasternak found that he could buy a tub created specifically for the purpose of cold plunging. About a year ago, he purchased a Plunge, a $4,990 plug-in tub that filters, circulates and sanitizes water in addition to cooling it down to 39 degrees Fahrenheit. Mr. Pasternak keeps it in the outdoor space at his workout studio and has since introduced it to his celebrity clients including Lizzo and Ashley Tisdale. Lizzo liked it so much that she bought one for her own home.

“It’s so cold I’m numb, but it helps my inflammation,” Lizzo captioned a video of her panting through an icy plunge on TikTok last month. She is not the only celebrity to show off a pricey home cold plunge recently.

And Gwyneth Paltrow, in a recent video to promote her Goop skin care line, highlighted the elaborate spa in her home in Montecito, Calif., noting the custom cold plunge. “Brad is an obsessive cold plunger,” she said, referring to her husband, the Hollywood producer Brad Falchuk.

The race to create and market the perfect at-home cold plunge is now on. Thomas Schiffer, the founder of Blue Cube, a company that sells cold plunges to individuals and commercial spas, called the competition in this burgeoning industry the “cold wars.”

Blue Cube’s offerings include a $15,999 Mini-Me cold plunge designed for home use and a $26,999 Malibu 56 model that can handle multiple plungers per day in a spa environment. The podcaster Joe Rogan has a Blue Cube model in his studio.

Both Plunge and Blue Cube started their businesses during the pandemic and said they have seen consistent sales growth. (Plunge got a boost after appearing on an episode of “Shark Tank” in May.) Other brands fighting for their piece of the market include Renu Therapy, which sells a Cold Stoic model for $9,699, and Morozko Forge, which sells a cedar-wrapped ice bath for $12,850.

“Being a new industry, it’s still kind of the Wild West,” said Mr. Schiffer, 52. “Our assumption is that this will be as ubiquitous as a sauna or a Jacuzzi. I’m hoping 10 percent or more of all pool, sauna, infrared sauna and Jacuzzi owners will buy an ice bath of some form.”

Ryan Duey, the 36-year-old co-founder and C.E.O. of Plunge, has similar ambitions. In five years, he said, he wants Plunge to be considered “the new Jacuzzi.”

Is spending several thousand dollars on a cold plunge necessary to get the — real or imagined — benefits of cold therapy? Probably not.

Lauren Schramm, a global Nike trainer and breath work and ice bath coach, said she uses regular old Rubbermaid tubs, water and bags of ice when she leads ice bath classes in Brooklyn.

Ms. Schramm, 30, charges $40 for a two-hour class that includes up to 15 minutes in the cold water (much less for beginners), breath work and community building. Though she is a regular cold plunger, she has not bought one of the more expensive models for herself.

“Cold water is cold water,” Ms. Schramm said. “You can turn your shower to cold when you’re in it, and you will get the same effect.” She added, however, that “if you have the funds, and you’re committed to the practice,” buying a cold plunge is more “sustainable,” because the water can be reused again and again. “If this is an investment that you would like to make, and it makes your experience of being in the tub better, awesome,” she said.

Remedy Place, a “wellness club,” has $50 ice bath classes, where up to three people can dunk together in side-by-side plunges for up to six minutes, while listening to their preferred pump-up music. The club offers a variety of wellness practices including infrared sauna and chiropractic work, but the founder and C.E.O. of Remedy, Jonathan Leary, said that most people know Remedy for its ice bath classes. He said the company plans to sell at-home units to the public in the future.

Ms. Schramm and Dr. Zaslow cautioned that cold-plunge newbies should speak to their primary care doctors before dipping into an ice bath for the first time. The biggest risk of cold exposure is hypothermia, Dr. Zaslow said, and there are also rare cases in which cold exposure can trigger cardiac arrest or arrhythmias, especially in people with underlying health conditions.

For some wellness influencers, cold plunging has become a way of life. Lauryn Bosstick, the entrepreneur behind The Skinny Confidential, has written about the power of ice on her blog for years, and she now sells $69 “Hot Mess” ice rollers for the face.

She also has two cold plunges at her home in Austin, Texas: a Blue Cube in her backyard and a Plunge in her bathroom. She said she reached out to both companies and now shares affiliate links for both models with her followers.

“What I’ve realized about the cold plunge, specifically, is that it’s the hardest thing, hopefully, that I’m going to do all day,” Ms. Bosstick, 36, said. “To start your day with that, knowing that you’re doing the most mentally tough thing in the morning, it makes everything else easier.”

Though she has a financial interest in getting her followers to adopt this practice, she allowed that most people can get the benefits of cold therapy for (almost) free.

“I think people will say, ‘Oh, well not everyone can afford an ice bath,’” she said. “OK, well then go Postmate ice — I’ve done this before — for $5 and put it in a bathtub with freezing cold water.”