Brighton, 6:45AM. The sky is clear and silent: blue blasted with streaks of white and apricot. We look out at the sea while another group leaves for the land. I make nervous conversation, hoping to stall the inevitable.
"How long do you normally go in for?"
"Five minutes, just to float around a bit." Rob cycles from his flat-share to the beach every day to get in the sea. When he can't, he takes a freezing cold shower for five minutes. In fact, on some days he takes two. These are harder, he says, due to how easy it is to turn off a shower. "Conditions are perfect," he adds, handing me a pair of neoprene boots and gloves. I strip down to my trunks and we begin our slow walk into the water.
The pain arrives almost immediately. My skin crackles and my chest starts to pump. I do my best to keep walking forwards, but I'm no longer able to watch Rob to my left. I retreat inside my own head, which is full of blaring sirens telling me to turn around. Instead, I drop down to my shoulders. The burning continues, only now black spots border my vision. My footing slips where the seabed banks; milky waves tower over me and for a moment I think I'm going to drop underneath, until the tide carries me a little closer to safety.
Then something starts to change. The longer I stay in the water, the more I settle. It's still Hell on Earth, but I start to hover above the experience, as though I'm watching my frozen pink body slosh about in the waves from a safe distance. After doing it a lot, Rob says he can observe negative thoughts kick in and then watch them pass by: "You realise how fleeting a stressful experience is. That you don't need to collude with it."
Wading back to the land, we return to our stuff and pull towels over our heads. I slide my feet out of the wetsuit boots. My bones feel rigid, but I can also feel a swelling of excitement.
Rob is part of a blossoming movement built on the principle that repeated exposure to cold water changes the way the body deals with stress. Its disciples say daily swims or cold showers give them a rush that lasts hours, and in some cases dramatically improves their ability to manage depression.
Raised in the Midlands, before moving to the Lake District as a teenager, Rob had long battled with low moods, OCD and an unhealthy relationship with alcohol. He first considered cold water after watching a TED talk on the virtues of daily cold showers. "I was so motivated by that I said to my girlfriend, 'Right, I'm doing a cold shower now,'" he says. It was his mum, a wild swimmer, who suggested that, now he lived in Brighton, he try getting in the sea. He remembers the panic, the breathlessness, but then a serenity. "The feeling was like being at peace. Like I was taking on all the stress of the day in one go," he says.
Rebecca, a stay-at-home mum based in Wiltshire, felt the same. She's been in treatment for the best part of 20 years for depression that, at its worst, saw her confined to her house by agoraphobia. "Private, NHS, meds, no meds, talking therapies, CBT – you name it I've tried it," she tells me over the phone. Cold water has proven undoubtedly the most consistent way of controlling her mental health. "Having had these issues for so long, a lot of what you go through, you feel like you're slowly dying. Getting in the water is sort of the same, but you know it's not going to take your life. It's a safe and measured way of being in that state of mind but having some control over it."
Like Rob, the water is an essential part of Rebecca's daily routine. She drops her two sons at school and heads straight for a lake a 30-minute drive from her house. "You still get the same fear," she tells me. "As you go through the winter it gets colder and colder. I think we probably hit a peak last week, where it was so cold people were breaking ice to get to the water."
Cold water should be the enemy. Drowning remains the third leading cause of unintentional injury-related death worldwide, with current estimates standing at around 360,000 deaths a year. Yet, from baptisms to baths, people have been trying to heal themselves with water throughout human history, normally built on the principle that altering the body's temperature is the key to release or relief of some kind. This thinking is present in ancient Greek, Egyptian, Roman and Chinese medicines, and hydropathic institutions were popular throughout 19th century England, enjoying visits from many of the age's most influential figures, from Charles Dickens to Darwin. Brighton itself is a town built on the Victorian fixation with seaside bathing.
Recent renewed attention is owed in part to doctor and TV presenter Chris Van Tulleken. He first encountered the cold water effect in 2012 while filming a BBC documentary in the Arctic. After recording a segment exploring the body's physiological response to freezing water, he found it had an unexpected side effect. "For 24 to 48 hours after jumping in, I felt elated," he remembers. "The feeling stuck with me."
When researching his most recent series, The Doctor Who Gave up Drugs, a programme that sought to highlight conditions where patients were over-treated, he met a 24-year-old woman called Sarah, who suffered from depression but wanted to stop taking antidepressants. Chris's thoughts returned to the water. He wanted to find out if there was any evidence that cold swimming might help, so contacted Mike Tipton, professor in the University of Portsmouth's extreme environments laboratory. "Mike said, 'Yeah, there’s some good science, but it's all theory, it's unproven.'"
Together, the pair gradually introduced Sarah to cold water and then outdoor swimming. It was the start of a process that eventually enabled her to stop taking the medication she'd been on most of her adult life. The case study was published in BMJ Case Reports, making it the most high-profile validation so far of the links between cold water and mental wellbeing.
But the unanswered question remains: what is the link?
"There is no doubt that plunging a body into 15, 12 degree water is a stress," says Mike Tipton. "The body evokes the flight or fight response, which involves the release of stress hormones. You experience hyperventilation, your heart rate goes up, your blood pressure goes up. It's a stressful thing to do, so you get a stressful response."
This "cold shock response" is something the body gets used to; someone who swims in cold water every day will cope far better with the shock than someone trying it for the first time. Mike's team has also recently established that bodies which have adapted to cope with the stress of cold water also perform better at altitude. This cross-adaptation, he explains, suggests that if the body gets used to dealing with one stress, it might get better at dealing with another. "This is all speculative," he clarifies, "but it's not implausible to suggest that – whether the trigger is water, altitude or an argument – if you habituate that response in one scenario, perhaps it has a generic benefit."
The science around the benefits of cold water immersion, then, remains murky. While its enthusiasts claim it strengthens their immune systems and aids them in weight loss, the truth is we don't actually know what it does. Mike adds that the cold water effect could be a placebo; that it could be the sense of achievement or of being outdoors that contributes to the high. There's a chance that the phenomenon is simply an extreme evolution of the wellness cult that has long existed around wild swimming. "We've not really isolated the factor in cold water swimming that is doing the good," he says. "That's the real question in it all."
Chris Van Tulleken also makes a point of clarifying he doesn’t believe cold water swimming is a miracle cure. He is not against antidepressants, he adds, only he feels the evidence for their use is sub-par and that lifestyle measures are too often overlooked. "It's blindingly obvious to a huge number of people, including a lot of doctors, that many of our most common conditions are intimately linked to the way our society is structured and the way we live our lives," he says.
"Reconnecting with nature, doing lots of exercise, being less lonely and having a society that's more economically equitable for everyone: that would reduce rates of all disease and improve life expectancy."
If cold water provides hope for some, then it also signals the ways in which our society is structured to ring-fence happiness. Research recently found that the country's poorest people are often those with the least access to national parks. The same study also estimated that people from BAME communities account for about 1 percent of visitors to national parks, despite making up about 14 percent of the general population.
Rebecca recognises that her response to the water isn't purely chemical. Yet, she says, the myriad components are too tightly bound to pinpoint one thing that makes the experience so effective. "I know that if I swim on my own [as opposed to with the people she meets at her local lake], I still get that cold water buzz, but don't get that feeling of putting the world to rights," Rebecca says. "The circle isn't complete."
However, she can't ignore the singular rush and the feeling of infallibility that follows. The problem now, she says, is searching for water that's cold enough. Generally she finds showers too warm, and following an uncharacteristically sunny spring it's likely the lakes will soon be too hospitable as well. "I'm going to Scotland next week," she adds. "It's a family holiday, but I'm also going for my own reasons!"
Rob is now a trainee psychotherapist, midway through his masters. He's moving to Oxford in a few months to live with his partner and has already picked out a spot in the Upper Thames to continue his morning ritual. For Rob, cold water and depression – or anxiety – are forces to be understood, not fought. "It's about equipping people with the knowledge of how their brain works, and the things that they can do to make it work in the way they want," he explains. "Ways they can [find to] not see it as an enemy, but to be accepting of it, to work with it."
For what its worth, after my morning dip I feel gigantic for the rest of the day. The sometimes overwhelming details of my life are reduced down to what they actually are: tasks, websites and unanchored anxieties that would barely make sense if I tried to write them down. I continue the experiment for the next few days with cold showers, which – while admittedly less atmospheric – top up the sensation that whatever else is happening, the present moment is the one I should be worrying about. If nothing else, it seems that understanding pain goes a long way towards cooling it.
If you want to try cold water immersion, don't jump in a freezing cold lake on your own. You might die. Head here for advice.