A “cold shock” sounds unpromising, at least at first blush. Plunge into icy water, and, as you gasp for air, your heartbeat jumps, blood vessels constrict, stress hormones like cortisol, an immunosuppressant, surge and you begin to shiver. Yet the practice of regularly soaking in cold water is booming and has even become fashionable.
The movement’s biggest evangelist is probably Wim Hof, a Dutch athlete and health guru. Dubbed “The Iceman”, Mr Hof has stood in a container filled with ice for nearly two hours and has swum under ice for 66 metres—a world record. His popular Wim Hof Method (WHM) combines meditation and breathing exercises with frigid soaks (or cold showers). His website says that adherence to the WHM burns fat, reduces inflammation, strengthens the immune system, balances hormones, improves sleep and lifts the mood. By exercising the heart, vessels and muscles, it also supposedly remedies cardiovascular diseases.
That would be no trifle if true. And cold does speed up a body’s metabolism. It also reduces the painful inflammation that causes swelling, which is why cold packs are placed on injuries. But does cold-water immersion provide broad benefits? A study in 2014 of 12 practitioners of Mr Hof’s method found that, following a deliberate introduction of an infection, Escherichia coli, they experienced fewer flu-like symptoms than a control group. In a study in 2018 in which Mr Hof was subjected to mild hypothermia, the cold was found to activate brain areas that are associated with pain suppression and well-being.
The largest study of what Mr Hof and his followers call “power in the cold shower” was conducted in 2015. Researchers asked about 3,000 volunteers to either shower normally or end with a cold blast lasting 30, 60 or 90 seconds. A month later, those who had ended their showers cold had been absent from work for 29% fewer days than those washing normally. That sounds impressive. But it may have been a placebo effect, and in any case there was no difference in the number of days for which members of the two groups felt ill.
Researchers at the University of Bern in Switzerland wondered if cold immersions might boost “body sturdiness” by improving antioxidant and immune responses. For 22 young men following WHM, they measured blood pressure and “pulse wave velocity”, the speed at which ventricular contraction pushes blood through the body’s arteries. Their work, published in 2023, poured cold water on Mr Hof’s claim that WHM produces broad results in just ten days. It concluded that 15 days of WHM therapy “did not exert positive effects” on a range of parameters.
Research remains far too thin to be conclusive. Sample sizes have mostly been small. Researchers also struggle to isolate factors—a study of winter swimmers, for example, might end up measuring the effects of vigorous exercise, not cold. That said, the effects of cold-water immersion on mood seem promising. Studies have shown cold dunks to raise levels of dopamine and endorphins, neurotransmitters linked to pleasure. A study in 2023 of 33 adults given a five-minute chilly bath and a brain scan found that they “felt more active, alert, attentive, proud and inspired and less distressed and nervous”.
That finding, at least, seems to justify the movement’s enduring popularity. For those seeking a break from the pampering of modern life, cold water can be ruggedly seductive.■
Curious about the world? To enjoy our mind-expanding science coverage, sign up to Simply Science, our weekly subscriber-only newsletter.