In 2024, researchers published the most carefully designed comparative trial to date on whether cold showers help depression. They split 84 women with elevated depressive symptoms into two groups: one practised Wim Hof-style fast breathing followed by cold showers; the other practised slow breathing followed by warm showers. After three weeks of daily practice, both groups showed a 24 per cent reduction in depression, a 27 per cent reduction in anxiety, and a 20 per cent reduction in stress. The difference between them was not statistically significant.
That is a strange finding for an ice bath company to lead with. But what the researchers found when they looked deeper changed the question entirely — and the real answer is more interesting than the headline.
What the Blades study tested
Robin Blades and a team led by Elissa Epel, a professor of psychiatry at the University of California, San Francisco, designed the trial during COVID lockdowns, with participants following guided 15-minute audio sessions each morning for 21 consecutive days. The cold group used the Wim Hof Method: cyclic hyperventilation breathing, breath holds, then a cold shower. The warm group used slow-paced breathing at six breaths per minute, then a warm shower at their preferred temperature.
Both groups showed clinically meaningful improvements on every primary measure. The researchers had expected the cold protocol to outperform, but it didn’t — outcomes with slow-paced breathing were, as the study noted, stronger than anticipated.
Two details deserve more attention than they typically receive, and both favour the warm group.
All six participants who dropped out came from the cold group; nobody quit the warm protocol. If warm showers produce the same primary outcomes, that dropout asymmetry matters for anyone deciding what to do.
And participants in the warm group rated their intervention as more credible. They believed in it more, liked it more, and found it more pleasant. In a world where adherence determines whether something works in practice, these are not trivial findings.
The practice, not the temperature
Both groups shared something that easily gets overlooked: a daily, structured cold water routine that lasts involving deliberate breathing and intentional engagement with the body for 15 minutes every morning.
Breathwork alone is a meaningful intervention: a 2023 meta-analysis of controlled breathwork trials found that structured breathing exercises produced small-to-medium reductions in stress, with the strongest effects from slow-paced techniques — exactly what the warm group was doing.
Epel’s framework centres on hormetic stress: short, voluntary exposures to biological challenge followed by recovery. “The practices create short-term spikes of biological stress followed by recovery, ease and deep restoration and that is otherwise hard to get,” she has written. Cold water creates that spike, and so does controlled breathwork. The daily ritual of showing up, breathing with intention, and engaging with mild physical challenge creates a recovery loop regardless of temperature.
What cold uniquely did
The Blades study measured more than depression, anxiety, and stress — it also tracked rumination, the repetitive, self-focused negative thinking that characterises depressive episodes, and here the two groups diverged.
Participants in the cold group showed a significant reduction in rumination after daily stressful events, but the warm group did not. Cold exposure appeared to interrupt the cognitive loop that follows a bad day: the replaying, the self-criticism, the spiralling analysis of what went wrong.
A 2011 longitudinal study tracked patients who had recovered from major depressive episodes and found that post-treatment rumination levels predicted who relapsed over the following twelve months, even after controlling for the number of previous episodes and residual symptoms. Researchers who study depression relapse have known this for years: it is not the sadness that brings people back into a depressive episode, but the thinking about the sadness — the recursive loop of negative self-referential thought that acts as the engine of relapse.
Cold water appears to break that loop in a way that warm water does not. You cannot ruminate in a cold shower — ice baths don’t reduce stress, they train it because your body has other priorities. And the Blades data suggests this interruption carries over into how participants responded to stressors throughout the rest of their day, not just during the shower itself.
The three-month picture
A larger trial extends the picture. A 2025 pilot study led by Epel and colleagues enrolled 141 women across four intervention arms and measured outcomes not only at three weeks but at three months. At three weeks, the familiar pattern held: all groups improved, with no significant differences between them.
At three months, the picture shifted. In the as-treated analysis, participants who had practised the Wim Hof Method showed better maintenance of their depression reduction compared to other groups — the initial improvements faded less.
A caveat matters here: an as-treated analysis introduces selection bias. The people who stuck with WHM for three months may have been more motivated or more suited to it. The finding does not prove that cold exposure causes better maintenance. It shows that among people who kept practising, the cold protocol held up better.
But taken alongside the rumination data, a coherent picture forms. What cold appears to do is not produce bigger initial improvements but create ones that are stickier, possibly because it addresses the mechanism most associated with losing those improvements over time. Cold plunge stress relief can last 12 hours or longer, suggesting that the neurological effects of cold exposure extend beyond the immediate recovery period.
What the evidence doesn’t show
Any serious reading of this data must acknowledge its boundaries. The Blades study had no passive control group — no arm where participants did nothing — which means both groups may have improved partly through expectation, attention, or natural symptom fluctuation. Researchers at the University of Portsmouth’s Extreme Environments Laboratory have questioned whether the mental health evidence for cold water is robust enough to justify the claims being made around it. The evidence base is small, the sample sizes modest, and the mechanisms not fully established.
And there is one limitation that may be the most important: the Blades study did not measure water temperature. Participants took cold showers in their homes across the United States, during different seasons, in different climates. We operate in Bali, where the coldest tap water barely registers as uncomfortable by northern European standards. A “cold shower” in Arizona in August is a profoundly different physiological stimulus from a cold shower in Boston in January. The study compared protocols, not temperatures, and the cold may not have been particularly cold.
Whether full-body cold water immersion for depression — at a controlled temperature, with hydrostatic pressure and guided breathwork — would show a greater separation from warm water than home showers did is a question no study has yet answered. Research on cold showers and depression suggests that the neurotransmitter surge from cold exposure happens regardless, but the magnitude varies with temperature and duration.
What cold actually adds
The question was never really “cold or warm?” but rather: what does cold add to a daily practice that already works?
Cold reduces rumination — the recursive negative thinking that predicts whether depression comes back. And in people who persist with it, the benefits appear to last longer. For someone who is not just trying to feel better this week but trying to stay better over months, they may be the advantages that matter most. Understanding why a cold plunge feels so good involves these same neurological mechanisms that interrupt rumination and reset mental patterns.
The daily practice builds the foundation. Cold may be what keeps it from cracking.
