In a classic case of 'what doesn't kill you makes you stronger...' Stacey Morrison confronts her serious aversion to the cold and enters a cryotherapy chamber.

In a classic case of 'what doesn't kill you makes you stronger...' Stacey Morrison confronts her serious aversion to the cold and enters a cryotherapy chamber.

Wim Hof is part of the reason cold immersion therapy has become the hottest wellness trend of recent years.

His website claims his breathing technique along with daily ice baths can boost your immune system, improve your metabolism, relieve stress and improve mental health as well as a number of more specific claims around certain illnesses.

One of his millions of followers is Black Fern Sarah Hirini.

As well as doing ice baths for injury recovery, the international rugby player also just does daily cold immersion for general wellbeing.

"I suppose I fell in love with it straightaway and just the benefits that I felt from it," she told Healthy or Hoax host Stacey Morrison.

She said it resets her body to enable her to thrive throughout the day.

Part of the charm for Hirini is the challenge.

"It's like a love/hate relationship," she said, "Every morning I'm like oh yeah, it's so good for me and then as soon as I go to hop in or turn on cold I'm like, oh, do I really want to do this? Is it really worth it?"

"There's constant questions in your mind but then you do it and get out and you're like, oh yeah, that was amazing."

Cryotherapy isn't just one thing. The term encompasses ice baths and ice packs, but the most high-tech treatment involves dry ice and a cryo-therapy chamber.

There is only one of these treatment facilities in New Zealand, on Auckland's North Shore.

Three minutes in the cryo chamber at Cryo Health Solutions will cost about $70, but owner Jill Somerville recommends a series of visits.

She said the freezing temperature causes receptors in the skin to react, creating a fight or flight-type response which results in blood being diverted to the vital organs. While the blood is sitting in your core it is getting pumped full of oxygen, enzymes and nutrients which then circulate back through the body as you warm up.

Somerville told Stacey Morrison the treatment is good for people with muscle pain or injuries, sleeping problems or anyone looking for a bit of a general pick-me-up.

"Honestly almost everybody that has come in and tried it has felt some sort of benefit," said Somerville, "Usually within that first hour, you get that endorphin rush, so people feel very energetic. It's a little bit of a mood booster."…

Go to this episode on rnz.co.nz for more details