A plunge into ice-cold water might sound like just the thing on a hot summer day, but there’s more to the art of cold plunging than that. Hot springs and sports recovery centers are offering cold plunges as a therapeutic activity, while fans are doing the same at home or in groups.

In fact, the Global Wellness Institute noted in its 2023 Hot Springs Trends report that, “The benefits of hot-cold contrast bathing have been widely recognized and is now almost universal in hot springs across the globe.”

Jim Mikula, senior vice president for WorldSprings, the company behind Iron Mountain Hot Springs in Glenwood Springs, says the institute “led the charge” by promoting hot springs and cold plunges — also referred to as contrast bathing — starting 20 years ago.

But “in the last four years it’s become really popular,” he said. “You feel refreshed, have more energy, and can almost see better when you go from the hot water to the cold.”

The institute explains the benefits this way: “Guests are seeking active ways to boost their immune system, reduce inflammation and find relief from pain: The combination of heat (in the form of bathing and saunas) and cold (in the form of cold plunges, ice showers and ice caves) provides an evidence-based way to achieve it.”

Others credit Wim Hof, a Dutch extreme athlete who has promoted “cold body therapy,” such as ice baths and cold showers, for the recent popularity of getting very chilly. He has written books about being “The Iceman” and features tutorial videos on his website.

Jumping into freezing cold water for a swim or soak goes back many years in Nordic cultures, but what started as a trend in the U.S. only recently seems to be here to stay with more people willing to take the, er, plunge and get the health benefits with consistent exposure to the cold.

“I’ve been fortunate that early in my career I participated in a sweat lodge and we could get out right in a stream with the water about 40 degrees,” Mikula recalled. “This is similar to the contrast bathing. When you’re in the hot water of about 100 to 104 degrees Fahrenheit, your blood is rushing to your skin to help cool you down, then when you get into the cold plunge, your blood reverses to protect your organs and this helps your parasympathetic nervous system so you feel comfortable, at ease, and relaxed.”

Denver Sports Recovery offers even more extreme versions called cryotherapy: for less than three minutes, someone in only underwear immerses all of their body except their head into a chamber with nitrogen set at 240 degrees below zero; professional athlete-style contrast therapy going from a 52-degree cold water tub to a 104-degree hot water tub; right after exiting, about 10 minutes in the heated dry sauna, a dip in the cold plunge with water that is 38 degrees Fahrenheit for four minutes and back and forth.

“It’s the bio-hacking world where we try to better ourselves,” said Shawn Caldwell, owner of Denver Sports Recovery. “If you shock the body into survival mode, it tricks your system, and it’s a little bit of a mental exercise.”