Brace yourself: the icy science of cold water immersion.

Winter is here, in fact we just shivered through the solstice. Which means it’s time to strip down, grit your teeth, and ask the question: is jumping into freezing water actually good for you, or are we all just performing wellness theatre for Instagram?

('Gettin' chilly with it: Hobart 2024)

(First published on my Substack where you can get #NerdNews, marvellous maths and general geekery.)

My stone cold credentials.

When it comes to the trend sweeping the world, I can’t say I’ve exactly dived in. I’ve taken two ice baths in my life, a two minute plunge at a science festival in Hobart, and a 5 minute immersion a couple of months ago that I’m still proud of.

Oh, and I did dive off a cruise ship in Antarctica and cold plunged for the best part of 8 seconds!

But the craze is here.

Inspired by everyone from the ice man himself Wim Hof, Chris Hemsworth getting his god-like nipples erect in the arctic or Lady Gaga swearing it helps treat her fibromyalgia, you can’t walk along Bondi beach at sunrise without sidestepping literally hundreds of people gettin’ their freeze on.

Simple question. Does it do anything?

As NerdNews so often finds, simple questions have anything but simple answers.

Ice Ice Baby: the arguments for.

Cold water immersion does one thing very reliably: it hurts. But beneath the suffering, something interesting is happening in your body. Immersion in water around 10–15°C triggers an almost immediate neurochemical response. Plasma noradrenaline reliably surges — studies clock two- to five-fold increases, the best-documented effect of the lot.

(Ice ice brainy: created via imagen)

Dopamine is the one the wellness feeds love to cite, but the evidence is thinner: the foundational 1996 study found a numerical rise that didn’t reach statistical significance, and some winter-swimming work finds no change at all.

“Cold-water immersion triggers the release of important hormones and neurotransmitters, such as dopamine, serotonin, cortisol, norepinephrine, and β-endorphins, which are all linked to modulation of the neural responses to stress and other emotion-related circuits affected in depression, anxiety, and posttraumatic stress disorder.”  — Journal of Neuropsychiatry and Clinical Neurosciences, 2024.

That’s the mechanistic picture some neuropsychiatrists are now sketching. A broad hormone and neurotransmitter cascade that might intersect with depression, anxiety and PTSD circuits. What is genuinely well documented is the acute noradrenaline surge. The leap from that to treating depression, anxiety or PTSD is where the evidence thins out, and at this stage that clinical payoff is a hypothesis, not proof.

Advocates say these sorts of hormonal releases help the body combat those ailments. The evidence is mixed, and we’ll get to that soon. The evidence for meaningful benefit in depression or anxiety specifically is the most speculative of all the claims made for cold water. As far as I can tell, no robust randomised trial has demonstrated it.

For athletes, the evidence is more concrete. A 2023 meta-analysis of 44 studies found cold water immersion is more effective than passive recovery for reducing muscle soreness in athletes, though protocols and effect sizes varied.

You might know DOMS (delayed onset muscle soreness) by name. But if you’ve ever walked downstairs in a hunched shuffle the morning after a brutal leg day, you’ve sure felt DOMS.

Well a 2025 network meta-analysis found that medium-duration immersion at moderate temperatures (11–15°C for 10–15 minutes) significantly reduced DOMS markers and improved explosive performance like jump height.

“That’s one of the methods that when I’m in heavy-duty training, I try to find. Mike will fill up my bathtub in the hotel room with all ice. Ice and water. We’re just always trying to figure out ways that even if it’s not there for us the way we’re accustomed to, we can figure it out.”  — LeBron James, Nike Trained podcast.

Wow. Wish I had a Mike!

And for the non-Le Bron?

The general population picture is patchier, but there’s a bit of data there.

One of the most comprehensive studies to date — a 2025 University of South Australia systematic review published in PLOS ONE — analysed 11 randomised controlled trials involving 3,177 participants. It found that in healthy adults, cold water immersion was linked to a reduction in perceived stress about 12 hours after immersion, with one trial suggesting modest improvements in sleep quality and short-term quality-of-life scores.

The cold hard truth: the arguments against.

Here’s where it gets uncomfortable — and not just because your bits are shrivelling.

For a wellness trend that has taken over social media, gyms, and expensive home installations worldwide, the science is surprisingly thin.

That headline PLOS ONE meta-analysis? It found no significant pooled effect on mood scores in randomised trials of healthy adults, and no significant acute effects on immune markers. The one tentative positive on the immunity front: a single cold-shower trial reported a 29% drop in self-reported sick days, though that’s one study leaning on self-report.

And it identified only 11 qualifying studies from a starting pool of 3,481. The vast majority of cold water immersion research doesn’t meet the methodological bar for a rigorous review.

Inconsistent water temperatures, varying immersion depths, wildly different durations, and no agreed protocol mean many of the studies can’t meaningfully be compared.

Then there’s “healthy user bias.” People who are up at sparrows, stripped down and ready to cold plunge tend to already exercise regularly, eat well, and sleep enough.

Unpicking whether the cold water is doing anything, or whether you’re just looking at the baseline health of people who do hard things, is genuinely difficult. CBC’s 2024 investigation into the science noted this as one of the central unresolved methodological problems.

Personally, I’m surprised there hasn’t been a cohort of more rigorous study done here. Any sports science grads might want to look at a P-H-D in I-C-E.

And sometimes ice ain’t nice!

And here’s a counterintuitive finding you don’t hear all often. If you’re lifting weights to build muscle, post-workout ice baths may be ‘unbuffing’ you.

A 2024 meta-analysis in the European Journal of Sport Science found that cold water immersion after resistance training may modestly blunt muscle hypertrophy.

In studies where every session was followed by 10–20 minutes of cold immersion, gains in muscle size were smaller, though both groups still grew and the evidence quality was only fair.

The inflammation your body produces after lifting is part of the repair and growth signal. Could it be that routinely dunking yourself in ice dampens the precise process that pumping iron is encouraging.

“Cold-water immersion has been extensively researched and used in sporting contexts to help athletes recover, but despite its growing popularity among health and wellbeing circles, little is known about its effects on the general population.”  — Tara Cain BHSc, University of South Australia, 2025.

Freeze a jolly good fellow.

So where does that leave us, gritting our teeth and about to plunge into an ice filled garbage tin at 6am?

The honest answer is that cold water immersion probably does something. There seem to be small but measurable effects on stress, sleep and quality of life in healthy adults, plus more consistent benefits for short-term recovery in athletes.

But the evidence base is still thin and the findings are messier than your Instagram feed suggests. The noradrenaline hit is physiologically documented in repeated studies, even if we can’t yet say with confidence how long it lasts or how much it matters for your day.

However, based on the best trials we have, it probably isn’t the immunity inspiring, depression destroying, metabolic miracle, that fills your feed.

Lady Gaga uses ice baths to manage in a specific therapeutic context. To blunt the chronic pain of fibromyalgia.

LeBron James swears by it, but the dude sleeps in his own portable hyperbaric chamber to control the precise percentage of oxygen he inhales.

Chris Hemsworth swam in Arctic water for a Disney+ documentary and called it “one of the hardest things” he’s ever done. But I’ll be honest, if I had Chris Hemsworth’s bod I’d also be getting semi naked every chance I had.

Osher and Wim!

None of this is quite the same as recommending you replicate it in a Bunnings tub before work.

“I never expected this to take that direction. We’ve got a lot of catching up to do.”  — Professor François Haman, University of Ottawa cold exposure researcher, NPR, 2023.

The science is still catching up to the hype. Which means the 90,000 ice bath tubs sold on Amazon in a single month in late 2023 were bought on faith as much as evidence.

That’s not a reason to avoid cold water. If it makes you feel good, helps you recover, or just gives you something to be proud of and some buddies to hang with at 6am, those are good things in and of themselves. But it is a reason to be sceptical of anyone selling you certainty alongside the ice.

And there is one non-negotiable caveat. Sudden cold immersion can sharply raise heart rate and blood pressure, so if you have cardiovascular disease or an arrhythmia, get medical clearance first, ease in gradually rather than leaping, and don’t plunge alone.

Winter is here. The ocean is cold. Jump in if you want to. Just don’t expect science to hand you a warm fluffy towel on the other side.

Further reading:

Cain et al. (2025), Effects of cold-water immersion on health and wellbeing: A systematic review and meta-analysis, PLOS ONE — link

Piñero et al. (2024), Throwing cold water on muscle growth, European Journal of Sport Science — link

NPR Health Shots (2023), Ready to cold plunge? We dive into the science to see if it’s worth it — link

CBC News (2024), Cold plunges are all the rage. But what does the science say? — link