Evidence yet to back up claimed benefits of cold water therapy

Australia Broadcast Center

06-05-2025

Every week in the UK, thousands of mostly middle-aged women take the plunge into freezing cold seawater.
Members of the "Bluetits Chill Swimmers" say the initiative has drastically improved their lives, but the jury is still out on the benefits of cold water immersion (CWI).
From ice baths to cold showers, the claimed benefits of CWI are prolific; a strengthened immune system, anti-inflammatory effects, mood boosts and improved sleep, among others.
But experts say there is more evidence for the harmful nature of CWI than its benefits — the nature of which remains "speculative" and "anecdotal".
Claims made lack quality evidence, research
In a paper published earlier this year, a group of researchers from the University of South Australia sought to answer the question of whether science supports the cold water fad.
Given that the benefits of CWI are increasingly marketed to the public, they looked for studies on the general population (rather than elite athletes).
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They found just 11 papers considered "quality" enough to include, with a range of conflicting findings.
Researchers were unable to find any evidence of mood improvements, but some evidence for decreased stress levels (albeit only 12 hours after CWI).
They likewise failed to find any evidence of a positive impact on immune function.
But in a quirky finding, one of the 11 studies concluded that those who underwent CWI had a 29 per cent reduction in sickness absence. There was a twist, however: while this group took less leave from work, they reported being ill for the same number of days as other participants.
Tara Cain, a research assistant and lead author on the project, admits this is difficult to interpret.
"It could be that they had better resilience or willingness to push through, just based on their involvement in the trial," she said.
Four-time Formula 1 world champion Max Verstappen in an ice bath.
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Mark Thompson: Getty Images
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"We don't want being part of a study to affect how people act in their general life, but they could have wanted to make the effort to keep going to work, even if they were sick."
The research team also found some evidence of improvements to sleep quality when CWI was combined with heat training, as well as self-reported quality of life measures, but Ms Cain cautions against drawing too much from their analysis.
There was no consensus among the papers, for example, on the method of CWI (e.g. ice baths vs cold showers), duration of CWI or cold water temperature, while only one study included female participants.
"I think the overarching message from this study is that there's such limited evidence out there that needs to be explored more to apply to the general population," Ms Cain said.
"Most of the information that's out there on social media is word of mouth, and anecdotal evidence.
"
A lot of [beneficial] claims made don't have that evidence-based research.
"
Just one 'proven' positive impact of cold water immersion
Mike Tipton, a cold water expert from the University of Portsmouth in the UK, agrees there is little evidence to support the "positive" impacts of CWI.
In fact, Professor Tipton is comfortable claiming just one "evidence-based" benefit of CWI: "perceived mental health benefits", as illustrated in the example of the Bluetits.
The Bluetits Chill Swimmers are a popular group in the UK.
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Supplied: Bluetits Chill Swimmers
)
"I've had some of the Bluetits ladies come up to me in tears telling me how this has changed their life, how they used to have mental health problems and don't have them anymore," he said.
"The problem with that is that the evidence is anecdotal. Anecdotal evidence is still evidence, but it's the weakest form.
"It's fine if that's what they want to do: I'm definitely not the fun police … but I want to make sure that I give them information to make sure they can do it as safely as possible.
"And as a scientist, I want to understand: what is the mechanism [that produces the effect]?"
Unfortunately, Professor Tipton says, there is much more evidence for how dangerous CWI is (than how beneficial).
As he explains it, human beings are "tropical" animals who ideally want to exist naked, in 26-28 degree air.
Taking that animal and plunging it into cold water (which he defines as 15 degrees Celsius or lower) induces a state of physiological stress termed "cold water shock".
A lot of evidence around cold water immersion is anecdotal.
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Costfoto/NurPhoto via Getty Images
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At worst, cold water shock is a precursor to drowning and cardiac arrest. As a standard occurrence, it will produce an acute inflammatory response.
"The body responds with a 'fight or flight' response driven by the sympathetic nervous system … [because] as far as it's concerned, it's under attack," Professor Tipton said.
'Habituation' to cold water could help with other stressors
As dangerous as cold water shock can be, it's also what might drive the potential "benefits" of CWI.
Repeated exposure to cold water, Professor Tipton explains, might "habituate" the body to this type of inflammatory stress response, with potential future benefits.
"Habituation is a decreased response to repeated stimuli… and a reduction in the alerting response that you get," he said.
Most people will have their "worst" reaction to an ice bath the second time they try it — because they're well aware of how cold it's going to be.
England footballers Alessia Russo and Lucy Bronze in an ice bath.
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The FA via Getty: Naomi Baker
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"After that, their 'stress' response will start to decline to the point where it's generally halved with about six three-minute immersions," Professor Tipton said.
Theoretically, he adds, CWI could be beneficial if the body learns to adapt this habituation response to other types of stress.
"At a cellular level, it may make you more resilient to stressors that evoke those kinds of responses," he said.
At present, however, he can point to only one study that lends weight to this theory.
His team conducted an experiment where they looked at people's responses to training at altitude.
They split participants into two groups, with both exercising in an altitude chamber. One group then did repeated warm water immersions, and the other did cold water immersions.
The cold water group performed much better in the second altitude training session than the warm water group.
Participants in Toronto's "Polar Bear Dip" where the water temperature is about 3 degrees Celsius.
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Julia Cherkasova: Getty Images
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"So the hypothesis is that the benefit that comes from cold water immersion is that physiologically you can habituate to stress. You become less responsive to those stressors, and maybe that generalises to other stressors."
As promising as the "habituation" theory may be, Professor Tipton warns that the evidence base is still largely "speculative".
Effects of cold water immersion could be 'placebo'
It's also possible that CWI could be subject to placebo effects.
Professor Tipton references a study from 2023 that looked at whether athletes who underwent CWI after a soccer match would see improvements in their recovery outcomes.
The athletes were split into three groups. One group underwent CWI, one group simply rested, and one was given a placebo: a drink they were told had been shown to reduce inflammation and improve muscle recovery.
Both the CWI
and
placebo groups showed improvements in recovery over the "rest" group, suggesting CWI may be no better than placebo (but still produces an effect).
According to Professor Tipton, the question of whether CWI is better than other forms of "active" recovery (such as walking, or yoga) is also unanswered.
As he puts it, this is the problem with most claims on the "benefits" of CWI: we still don't understand the "mechanism" behind its positive effects.
Going back to the anecdotal claims of the Bluetits Chill Swimmers, Professor Tipton argues there are many beneficial factors at play:
"Nobody has really done properly controlled studies to isolate the active ingredient in the experience of going for a dip… is [the benefit] coming from green therapy, blue therapy, exercise, meeting people, having cake and coffee, or all and any of those?"