Deliberate cold as stress training: the 11-minute weekly dose

The Short Version

Across five conversations, one idea keeps coming back: deliberate cold is a stressor you choose, and practicing calm inside a chosen stressor trains the nervous system to stay steadier when stress arrives uninvited [2][3][4]. Dr. Susanna Søberg's study of Danish winter swimmers puts a floor under the practice: about "11 minutes in total per week" of cold, split into short dips over two to three days, ideally ending on cold so the body has to rewarm itself [1]. Andrew Huberman explains why it works on the mind: cold reliably floods the body with norepinephrine and epinephrine and also raises dopamine, so each session is a rehearsal of keeping the prefrontal cortex in charge while the body screams to get out [2][4][5]. Caltech neuroscientist Ralph Adolphs offers a personal case: after weeks of ice baths his heart rate and breathing dropped on entry, and his anger at a honking driver went "flat" [3]. The dose is modest and the target is discomfort, not extremes. Stay uncomfortably cold but safe, keep the bouts short, and treat it as training for bad weather rather than as a feat [1][2][4].

Table of contents

What They Said

Susanna Søberg: the minimum dose, and why discomfort is the point

Søberg did her PhD at the University of Copenhagen on how deliberate cold and heat affect human metabolism. She is first author of a 2021 study in Cell Reports Medicine that identified minimum thresholds for cold and sauna exposure needed to activate brown fat thermogenesis [1]. She did not come to the subject as a cold enthusiast. She describes herself as a former "cold sissy" who was always bundled up, and says winter swimmers on the jetty teased her that she could not study the practice without trying it [1]. Her first few dips were painful, but afterward she felt fantastic, energized and positive, and did three rounds with sauna [1]. Today she usually does one or two dips, once or twice a week [1].

The study design. For her proof-of-concept study she recruited men who had winter swum for two to three seasons, two to three times a week, staying in for one to two minutes, and matched them with a control group on factors like BMI and diet [1]. She studied only men because women have more brown fat, and including both sexes would have needed more groups than the unfunded study could support [1]. On swimming days, participants did three cold dips of up to two minutes and two sauna sessions at about 80°C for 10 to 15 minutes, starting and ending in cold water [1]. Water ran from roughly 12°C in October to about 2°C in January [1]. She measured brown fat with PET-CT and PET-MRI scans, infrared thermography, electromyography for subtle shivering, and a comfort scale [1].

The number. Added up, the swimmers' routine came to about "11 minutes in total per week" of cold and "57 minutes in total per week" of sauna, spread over two to three days [1]. Huberman's solo episode reports the same figure. Søberg told him the 11 minutes could be split into two, three or four sessions [2]. She ties the heat side to a 2015 Finnish cohort study of more than 2,000 sauna bathers followed for 20 years. It found a dose-response reduction in cardiovascular risk up to about 19 minutes per session, with no added benefit beyond roughly 30 minutes per session [1].

Her message is that you don't need extremes. Going past the healthy hormetic window, with 20 to 30 minute ice swims for example, can exhaust cells and push toward chronic stress [1]. The water doesn't have to be ice-cold either: 12°C water, or even 19°C air, can activate brown fat [1]. What matters is change. Get in, get out and get back in, and vary the temperature through the seasons or in your plunge. Changing temperature, she says, will "keep your cells on its toes" [1].

Discomfort, not a thermometer reading. Søberg doesn't prescribe a temperature. The target is to get uncomfortably cold [1]. The sign is the cold shock: a burst of sympathetic activation, a gasp reflex and hyperventilation, which fades with repeated exposure [1]. She is blunt that it should never feel comfortable: "It should be hard because that's the point of it," and "You should not enjoy it" [1]. How stressful it feels depends on the gap between skin temperature and water temperature, which is why stepping from a sauna into cold water feels easier than stepping in already chilled [1]. She adds that the more you avoid cold, the more painful it feels when you finally face it, and that people with more sensitive nervous systems may feel cold pain more [1].

Cold as a training center. Søberg explicitly frames cold as training. Cold, heat and exercise are forms of hormesis, a healthy stress that makes cells more robust by raising heat shock and cold shock proteins [1]. Cold water is "your cold training center" and the sauna is your heat training center [1]. She tells people not to fear shivering, as long as they avoid hypothermia, because shivering raises metabolism, burns calories and improves insulin sensitivity [1]. She sees modern life, with well-insulated homes and sedentary indoor habits, as having removed natural temperature stressors. She names cold, heat, exercise and some fasting as natural hormetic stressors that help restore balance [1].

End on cold: the Søberg principle. Huberman named the principle after noticing that her participants always finished in cold water [1][2]. Søberg explains that ending cold forces the body to rewarm itself. That keeps brown fat, muscles and neurotransmitters active for hours, so a one-to-two-minute dip becomes an extended workout [1]. After three to five sessions, she says, people notice a switch where they warm up more easily [1]. At rest, the winter swimmers in her study had warmer skin, and they lost heat faster through more responsive blood vessels [1].

What the study found. Winter swimmers shivered less vigorously than controls even when they reported feeling similarly cold. They produced less insulin while fasting and cleared glucose faster after a glucose test [1]. Huberman sums up that combination of lower insulin and better glucose clearance as "really what what we all seek" [1]. The team saw IL-6 rise alongside the anti-inflammatory IL-10 [1]. Søberg cites an earlier 2016 study of middle-aged men and women who winter swam for one season and afterward had lower blood pressure, a lower heart rate and better insulin sensitivity. She suspected brown fat was the missing link, which helped motivate her own research [1]. She regrets not measuring sleep. The swimmers anecdotally reported sleeping very well, while controls mentioned brief awakenings [1]. The swimmers were also noticeably at ease in the busy lab. One walked out of the bathroom completely naked after an eight-hour session [1].

The "brown fat negative" swimmer. One winter swimmer turned out to have no brown fat at all [1]. Before she knew it, Søberg noticed that he shivered early and struggled to regulate his temperature during the cooling protocol, and his insulin and glucose clearance looked more like the control group's [1]. He was excluded as an outlier, though including him didn't change the conclusions [1]. The case is a reminder that the same routine doesn't produce the same body in everyone.

Andrew Huberman (solo episode): the protocol, the chemistry and the walls

In his dedicated episode, Huberman opens with a safety message. Temperature is a potent stimulus, so consult a physician, progress gradually and look for the minimum effective dose [2]. He then separates the goals of cold exposure: mental resilience and stress control, mood and focus through catecholamines, metabolism, reducing inflammation, and physical performance [2].

Why "deliberate" matters. Huberman stresses the word deliberate. Citing his colleagues David Spiegel and Alia Crum, he says that choosing to put yourself in a stressful state, and believing it is beneficial, produces different physiological effects than stress imposed on you. He distinguishes this mindset effect from placebo [2]. That is the heart of this insight. The value lies partly in the cold itself and partly in the fact that you chose it.

How cold. Because tolerance varies so much, his rule is that the temperature "should place your mind into a state of whoa I would really like to get out of this environment but I can stay in safely" [2]. That threshold changes from day to day and within the day. Cold feels much harder late at night than in the afternoon [2]. He warns that plunging into extremely cold water, such as through a hole in lake ice, can cause cold shock and even death in unprepared people [2]. As for method, immersion up to the neck with hands and feet under is most effective. Cold showers come second (they are barely studied because they are hard to standardize), and going outside underdressed comes third [2].

Resilience, defined. Cold reliably releases norepinephrine and epinephrine, from the adrenal glands, from brain areas such as the locus coeruleus and from elsewhere in the body, no matter how tough or experienced you are [2]. Since everyday stress runs on the same chemicals, deliberate cold lets you practice staying calm and clear-headed while flooded with them [2]. His operational definition, in his own words: "you are able to resist escape from the stressor, the cold by virtue of your willpower, which is really your prefrontal cortex causing top down control on your reflexes and your limbic system and your hypothalamus" [2]. The payoff: "you are basically getting better at controlling your behavior when your brain and body are flooded with norapinephrine and epinephrine" [2].

Two ways to progress. The first is timed progression, like sets and reps: one minute on Monday, 50 percent longer on Wednesday, twice as long on Friday, then keep extending the time or lowering the temperature [2]. He calls it "very objective" and says "You could even log it in a book" [2]. Its weakness is that you eventually run out of room, because water can only get so cold and you can't sit in it all day [2]. His preferred method is counting walls: the surges of "I don't want to do this" and the urge to get out [2]. For some people, getting in at all is the first wall. Decide before you start how many walls you'll climb that day, such as three or five. Each wall arrives when it arrives, and you vary the number and the temperature over time [2]. This keeps the stimulus effective and mirrors real-life stressors, which arrive unpredictably, like a text with bad news [2].

Mindset and the working brain. He compares mindset in the water to driving on gravel roads: sometimes you speed through and sometimes you slow down [2]. You can calm yourself with double inhales through the nose and long exhales through the mouth, or lean in and grind it out [2]. Everyone gets short of breath in cold water, and he says frontal cortex function can drop 30 to 80 percent [2]. Doing mental tasks in the cold, such as challenging arithmetic, forming full sentences or recalling difficult information, trains the prefrontal cortex to stay online under stress, much like the odd sport of chess boxing [2]. He also notes that sitting perfectly still lets a warm thermal layer form around the body. Moving your limbs, with hands and feet submerged, breaks up that layer and makes the same temperature a stronger stimulus, so people who sit stoically are shortchanging themselves [2].

The 11-minute target as a floor. Huberman says a few human studies point to about 11 minutes total per week, split into two to four sessions of a few minutes each. He notes that this threshold is tied mainly to metabolic effects and suggests treating it as a minimum [2]. Once 11 minutes becomes easy and you rarely hit walls, safely lower the temperature, extend the time or increase the frequency [2]. His own practice is about three sessions a week of two to six minutes each, using the walls method, for roughly 11 to 15 minutes in total [2]. Consistency and safety matter more than precision [2]. He points out that Navy SEAL training relies on cold water precisely because it gives wide room to adjust duration and temperature, unlike heat, where the margin before injury is small [2].

Dopamine: why people feel good afterward. Cold is unusual among stressors because it raises dopamine, not just norepinephrine and epinephrine [2]. He details a 2000 study by Šrámek and colleagues in the European Journal of Applied Physiology. People sat immersed to the neck for one hour at 32°C, 20°C or 14°C. The 32°C group showed no significant change, and the 20°C group's metabolic rate rose 93 percent. In the 14°C group, metabolism rose 350 percent, norepinephrine 530 percent and dopamine 250 percent, and the increases lasted up to two hours afterward, when measurements stopped. Cortisol did not rise significantly [2]. Huberman says the dopamine rise is comparable to that of addictive substances like nicotine, but without the crash [2]. He is careful to add that he is not recommending an hour of cold, and that shorter, colder exposures have not yet been studied the same way [2]. From the transcript: people say "it was stressful. I didn't enjoy it, or I eventually grew to like it, but that I always feel better afterwards. And then that feeling lasts a very long period of time" [2]. He considers it "almost certain" those reports relate to the dopamine increases, and that together with norepinephrine they explain the reported gains in mental acuity and focus [2]. He mentions that psychiatrist Anna Lembke describes, in Dopamine Nation, a patient who used cold water as a healthier dopamine source to help stay sober [2]. Citing Hans Selye's distinction between distress and eustress, he suggests deliberate cold produces eustress: catecholamines rise without much cortisol [2].

Layering. Being fasted already raises norepinephrine and epinephrine, which may amplify the effect. He adds, "I certainly wouldn't recommend doing it with a very full stomach in any case" [2]. Taking about 300 milligrams of caffeine 60 to 120 minutes beforehand increases dopamine D2/D3 receptor availability in the striatum, according to a human study, so the cold-induced dopamine can act more strongly [2]. He adds a sensible caveat: stack enough protocols and you would spend your whole day chasing a dopamine pulse, and you should always consider your cardiovascular health and blood pressure first [2].

Metabolism and the Søberg principle. Norepinephrine binds receptors on white fat cells and activates pathways including UCP1, PPAR-gamma and PGC-1 alpha. That increases mitochondria and changes gene expression, so white fat becomes thermogenic beige or brown fat [2]. Huberman calls the Søberg principle a key piece of data that "translates to something larger" [2]. As he puts it: "to achieve the greatest increases in metabolism through deliberate cold exposure you want to force yourself to reheat on your own after the deliberate cold exposure meaning you wouldn't want to go from the cold shower to a hot shower or from the cold shower to a sauna" [2]. He admits he usually takes a hot shower afterward because metabolism isn't his main goal: "in doing so I'm short circuiting some of the further metabolic increases that I would achieve were I to just end with the cold" [2]. He extends the principle to shivering. A 2018 Nature study found that shivering muscles release succinate, which activates brown fat thermogenesis [2]. A tough but effective routine alternates one to three minutes of cold with one to three minutes standing in the air, arms at your sides and not hugging yourself, until you shiver [2].

Timing and training. Cold on the body's surface ultimately raises core temperature and alertness. Doing it in the morning or midday supports the natural daytime rise, while late evening sessions can interfere with the temperature drop needed for sleep [2]. He advises cold only when you are prepared to be alert for the next one to six hours [2]. If muscle growth or strength is the goal, avoid cold immersion for about four hours after that training, or do it on a different day [2]. For endurance, sprint or skill work, he sees no reason in the literature to avoid cold right afterward [2]. He summarizes a 52-study meta-analysis finding that cold water immersion after high-intensity exercise improved muscular power, reduced soreness and serum creatine kinase, and improved perceived recovery at 24 hours compared with passive rest, though eccentric exercise did not benefit. It also found that shorter exposures at lower temperatures can be effective [2].

Andrew Huberman (with Lewis Howes): cold and breathwork as training for bad weather

On The School of Greatness, Huberman places cold inside a broader toolkit for stress [4]. His central claim is that there are two kinds of stress, hyper-alert stress and overwhelmed, exhausted stress, and each needs the opposite tool [4]. The organizing principle is that "It's very hard to control the mind with the mind" [4]. Trying, he says, "is like trying to grab fog" [4]. Instead, you work through the body. The phrenic nerve gives you a direct wire from the brain to the diaphragm, and breathing controls heart rate, which then lets you control the mind [4].

He describes the struggle as limbic friction. The limbic system drives the stress response, and the prefrontal cortex provides top-down control [4]. Real-time tools include the physiological sigh (a double inhale followed by a long exhale) and inhale-emphasized breaths for alertness [4]. But he separates these from offline practices that raise your stress threshold. As he frames the question: "how do I get calmer in the mind when my body is freaking out?" [4].

Wim Hof-style breathing. One offline practice is Wim Hof-style breathing, also called tummo: 25 or 30 rapid, deep breaths of deliberate hyperventilation, followed by an exhale and a breath hold, then an inhale and hold [4]. It raises heart rate and triggers adrenaline release from the adrenal glands [4]. In the hold, "what you're doing essentially is you're learning to be calm as your body is flooded with all this adrenaline and the heart rate is going" [4]. His lab now has more than 100 people doing different breathing experiments [4]. He calls this pattern "somebody training themselves how to self-induce stress," and says there is "good literature and some emerging science that's still ongoing" that it is possible to get comfortable in these agitated states [4]. He strongly warns never to do this near water, even a puddle, because people have drowned after passing out, and says people with lung problems should be careful [4].

The ice bath as the same drill. "The ice bath is another good example of this," he says, because "cold water will almost always induce a low level of stress in people" [4]. The inner dialogue is simple: "So the body is saying, this is really cold. This is really cold. Get out now. And you're pushing back on that and it's top down control. It's pure top down control" [4]. It doesn't get easy even for fans: "Even if you learn to love it, you're still after every time jumping in there, okay, I got to control the mind essentially to calm" [4]. He also mentions the "hour of pain," described by a friend who is a former special operations member: holding one position on the floor for an hour against an overwhelming urge to move [4].

Why the chosen stressor matters. This is where the "bad weather" framing comes from. Huberman compares this training to learning to drive in rain and fog in an empty parking lot rather than on the freeway [4]. He cites Stanford psychiatrist David Spiegel's point that what matters is not only the state you're in, but how you got there and whether you had anything to do with it [4]. In his words: "So when you self-induced stress and then you say, oh, I can calm my mind, even though my body is feeling agitated, that's a very positive experience for many people. Whereas when someone else is causing your stress and you're trying to calm down, it feels like you're battling 25 different things" [4]. He calls these "skills that anyone can develop," requiring "information of what to do, but zero training" [4]. Through neuroplasticity, people who practice such tools start using them automatically, sighing even before they cross the stress threshold [4].

Ralph Adolphs: the ice bath as emotion-regulation practice

Adolphs, a Caltech professor of psychology, neuroscience and biology, defines emotions by what they do. They are flexible control states between rigid reflexes and deliberate planning, marked by priority, valence, scalability and persistence [3]. He argues that most emotional difficulties are about regulation rather than the emotions themselves [3]. His main principle is that the earlier you intervene, the better, and that both the specific strategy and the automaticity of control can be trained [3].

His ice bath is an insulated horse trough on his porch, filled with 40-pound bags of ice [3]. He describes the adaptation curve in detail: "When I start, first week, it is terrible. Super painful. You know, you go in, it's like a whole body cold pressure task, right? Second week, it's also, you know, your breathing goes up, your heart rate goes up, but gradually, and kind of with some automaticity to it, now I go into the ice bath immediately. My heart rate goes down. My breathing goes down. I get super relaxed" [3].

The key point, for this insight, is that "It generalizes for me" [3]. Pasadena traffic had seemingly gotten worse. Once, while he was signaling to park, a driver pulled up behind him and leaned on the horn: "you immediately feel just an immediate anger response, right? Well, after the ice bath, it's flat" [3]. He interprets it as "an immediate automatic downregulation of my autonomic emotional response to a psychological stressor, to somebody honking at me, that was trained and generalized from the ice bath" [3]. He is explicit about the evidence level: "There's an experiment of one. I'm not claiming this as a published study" [3]. The goal, as he puts it, is that regulation becomes automatic: "You don't have to overthink it. It becomes smooth and effortless to some extent. And that's the place where you want to get" [3]. He even prescribes it, half-joking, for people drawn to outrage: "They should take ice baths" [3].

Huberman adds context in the same conversation. Years ago his lab collaborated with the special operations community, who value cold because "it's so reliable. You always get an increase in adrenaline, nor epinephrine in the brain" [3]. He also notes that "you get often reductions in cortisol, which is kind of paradoxical" [3]. He calls it "reliable and super efficient," and safe "unless you're doing it in a lake or you're doing hyperventilation first" [3]. The summary adds that there is some evidence cold improves resilience to later stressors [3].

Adolphs pairs cold with other regulation training. Ultrarunning trains regulation over longer time scales, through the sport's mantra of "relentless forward momentum" and his own version, "relentless optimism" [3]. His lab also opens Monday meetings with three to five minutes of silence, which newcomers find stressful at first but which he says is completely trainable [3]. His broader frame is variability: "Being able to switch and having lots of variability and training that is definitely beneficial. It's beneficial for just basic physiology is beneficial for emotion granularity and emotion regulation" [3].

Huberman at a live Q&A: discomfort sets the size of the payoff

At a live Q&A in Los Angeles, Huberman summarized cold exposure briefly. Stay in cold water until you reach significant discomfort, but not panic, and dopamine rises substantially, improving mood, motivation and resilience for hours [5]. The summary records his claim that the discomfort phase is essential and directly correlates with how much mood elevation follows [5]. The same session touched on palmar cooling, placing the hands or feet on cold surfaces between sets or tasks, as a separate performance tool [5].

Where They Agree, and Where They Don't

Agreement

Discomfort is the dose, not a temperature. Søberg says to get uncomfortably cold and uses the cold shock as the marker [1]. Huberman's rule is the "whoa I would really like to get out of this environment but I can stay in safely" state [2], and at the live event he said discomfort short of panic drives the mood payoff [5]. Nobody in these sources gives a single target water temperature.

Cold is training. Søberg calls cold water "your cold training center" and places it among hormetic stressors alongside heat and exercise [1]. Huberman compares timed progression to "sets and reps in the gym" [2] and cold-plus-breathwork to driving lessons in bad weather [4]. Adolphs describes a "direct autonomic training component" that makes regulation automatic [3].

Modest, repeated doses beat heroics. Søberg warns that 20 to 30 minute ice swims can exhaust cells [1]. Huberman treats 11 minutes a week as a practical minimum and says consistency and safety matter more than precision [2]. The two also agree, in their conversation, that splitting cold into short bouts is probably better than one long session. The benefit comes from the shock, and the autonomic response fades after the first few minutes [1].

The stress chemistry is reliable. Søberg describes the catecholamine release (noradrenaline, adrenaline and dopamine) [1]. Huberman says cold raises norepinephrine and epinephrine no matter how tough or experienced you are [2], and says special operations teams valued it because "You always get an increase in adrenaline" [3].

The response softens with practice. Søberg: the cold shock fades with repeated exposure, and the catecholamine response gradually softens [1]. Adolphs: after two weeks his heart rate and breathing went down on entry [3].

Tension and disagreement

Should you enjoy it? Søberg says "You should not enjoy it," and jokes that if you do, something is wrong [1]. Adolphs, by contrast, now gets "super relaxed" on entry [3]. Huberman's framing reconciles them. Even people who learn to love it still have to exert top-down control each time they go in [4], and his walls method says you should adjust temperature or time once you rarely hit walls [2]. The two positions may describe different stages. Relaxation on entry is the adaptation Adolphs was after, while Søberg's warning is that a session with no discomfort left is probably no longer a strong stimulus.

Ending on cold, or not. Søberg's principle is to end cold and rewarm naturally [1]. Huberman agrees that this maximizes metabolic benefit, yet still finishes with a hot shower because metabolism isn't his main goal [1][2]. The disagreement is really about goals. If your aim is resilience and mood, he treats ending warm as acceptable. If it's brown fat and metabolism, end cold.

Progress by the clock or by walls? Timed progression is objective and loggable, but it eventually hits a ceiling [2]. Counting walls is subjective but mirrors how real stress shows up, unpredictably [2]. Søberg's emphasis on variation, "keep your cells on its toes," is closer in spirit to the walls approach, though she frames it in cellular rather than psychological terms [1].

What the 11 minutes actually supports. This matters for the insight's central claim. Huberman says plainly that the 11-minute threshold is tied mainly to metabolic effects [2]. Søberg's study measured brown fat, insulin, glucose and thermal comfort, not stress resilience [1]. The resilience argument rests on mechanism (the same catecholamines drive everyday stress) [2], on the mindset research he attributes to Spiegel and Crum [2][4], on his lab's ongoing breathing work [4], on some evidence for improved resilience to later stressors [3], and on Adolphs's self-described "experiment of one" [3]. So 11 minutes is a sensible weekly floor for the stress-training use as well, but the sources don't show that it is the proven dose for calm.

Cortisol. In the Šrámek study, cortisol didn't rise significantly [2]. In the Adolphs conversation, Huberman goes further and says cortisol often falls, "which is kind of paradoxical" [3]. These are compatible, but the stronger claim comes without a specific study attached.

Long versus short exposures. The biggest dopamine numbers come from one-hour immersions at 14°C [2], a protocol nobody here recommends. Huberman himself notes that shorter, colder exposures haven't been studied the same way [2], while Søberg warns that very long cold sessions push past the healthy window [1]. The dopamine story and the dosing story therefore rest on different protocols.

Why It Works

The stress chemicals are the same ones

Cold activates the sympathetic nervous system and releases catecholamines [1]. Huberman names the sources: the adrenal glands, the locus coeruleus and elsewhere in the body [2]. Everyday stress runs on the same molecules, so time in cold water is time spent practicing behavior under that chemical state [2]. His definition of resilience, the prefrontal cortex exerting "top down control on your reflexes and your limbic system and your hypothalamus," describes exactly the skill being rehearsed [2]. In cold water, frontal function can drop 30 to 80 percent, which is why doing mental tasks while immersed trains the cortex to stay online [2].

Choosing the stressor changes the experience

Huberman, drawing on Spiegel and Crum, says a stress you choose and believe is useful produces different physiological effects than stress imposed on you, and that this is distinct from placebo [2]. With Howes he adds that mastering self-induced stress is "a very positive experience for many people," while fighting stress someone else causes feels like "battling 25 different things" [4]. Cold makes a good choice of stressor because it is highly adjustable. Navy SEAL training uses cold water precisely because duration and temperature can be dialed up or down with a wide margin before injury [2].

Regulation becomes automatic

Adolphs's model is that the automaticity of control, not just the strategy, can be trained [3]. His ice bath went from a spike in heart rate and breathing to a drop in both on entry, and the effect seemed to carry over to a road-rage moment [3]. Huberman describes the same arc with breathing tools: through neuroplasticity, people start using them automatically [4]. Søberg's physiological account matches this at the body level. The cold shock and catecholamine response fade with repeated exposure, and capillaries get better at constricting [1].

Dopamine makes the practice stick

Cold raises dopamine, which Huberman says explains why people feel better for hours afterward even when they hated being in the water [2][5]. In the Šrámek study, dopamine rose 250 percent and norepinephrine 530 percent at 14°C, with the effects lasting up to two hours [2]. Because cortisol didn't rise significantly, he classifies the result as eustress rather than distress [2]. At the live event, he tied the size of that mood lift to how much discomfort you tolerate [5].

Short bouts and ending on cold

The autonomic response is strongest in the first few minutes, so repeated short shocks deliver more stimulus than one long session [1]. Ending cold triggers the "after drop." Blood vessels that constricted in the water open during rewarming, warm blood cools at the skin and returns to the core, and core temperature falls further. That drives shivering, and shivering activates brown fat [1]. Shivering muscles release succinate, which activates brown fat thermogenesis [2]. Brown fat receives cold signals through three parallel pathways: from the hypothalamus via noradrenaline, directly from skin cold receptors, and from shivering muscle [1]. Norepinephrine can turn white fat beige or brown through UCP1, PPAR-gamma and PGC-1 alpha [2].

Longer-term physiology

With repeated exposure, brown fat cells gain more and more efficient mitochondria [1]. In her study, winter swimmers produced less fasting insulin and cleared glucose faster [1]. The 2016 season-long study found lower blood pressure, lower heart rate and better insulin sensitivity [1]. Cold lowers inflammatory cytokines such as IL-6 and raises anti-inflammatory IL-10, according to Huberman [2], while Søberg's team saw IL-6 rise alongside IL-10 [1]. Huberman links Søberg's work to his favorite framing, "biology is not an event it's a process," and to the goal of becoming "a very efficient heating and cooling system" [1].

Where It Applies, and Where It Doesn't

It applies when you can stay in control. The whole point is a controllable stressor. Huberman's threshold explicitly includes "but I can stay in safely" [2], and the live-event guidance is discomfort but not panic [5]. Ice holes in lakes and open water are where it stops being controlled. Huberman warns of cold shock and death in unprepared people [2] and flags open lakes and prior hyperventilation as the exceptions to cold's safety [3].

Never combine hyperventilation breathing with water. The Wim Hof-style breathing Huberman teaches for stress training must never be done near water, even a puddle, because people have drowned after passing out [4]. Keep the two drills separate.

Head dunking raises the stakes. Søberg cites Danish research showing that immersion to the neck at 0°C cuts blood flow to the brain by around 30 to 40 percent, and a Canadian review finding that dunking the head increases the rate of core heat loss by 36 percent. That deepens the after drop and moves you closer to hypothermia [1]. She leaves the choice to each person, with that information in hand [1].

Children lose heat faster. Because of their surface-area-to-mass ratio, children have to use their muscles to defend core temperature much sooner than adults [1]. Huberman recounts a 16-year-old who became hypothermic, slurring and disoriented, during a long Pacific swim without a wetsuit. He stresses always swimming with others and starting cautiously, with cold showers for example [1].

Sex differences. Women run colder, especially in the hands, feet and ears [1]. Søberg speculates that women might need less than 11 minutes a week, but says the protocol works for her and should be broadly similar for short exposures. Bigger differences matter mainly for long ice swims [1]. Her newer study includes both sexes, but its data are still being analyzed [1].

Raynaud's and sensitive extremities. Søberg knows of no studies on Raynaud's syndrome and has heard mixed reports [1]. She suggests keeping the hands out of the water and wearing neoprene boots. The rest of the body still gives a full activation, and she keeps her own hands out [1]. Note that this trades against Huberman's point that hands and feet under water is the most effective form [2].

Timing around sleep and strength training. Late-evening cold can interfere with sleep onset [2]. Søberg suggests testing on yourself whether evening sessions disturb your sleep, as you would with coffee or exercise [1]. Huberman did cold at 11 p.m. during a 30-day challenge and slept fine, but was exhausted on those days [2]. For hypertrophy and strength, keep immersion about four hours away from training [2].

People who dread it may gain the most. Huberman says people who dread the cold are ideal candidates, because a bigger stress response brings a bigger adaptation [1]. He also recalls elite military operators facing cold water. About a third went straight in, a third got through while visibly anxious, and a third wouldn't go past their knees or thighs [1]. Toughness elsewhere doesn't guarantee comfort here.

Individual biology varies. The "brown fat negative" swimmer followed the same routine without the same metabolic result [1]. Søberg studied only men [1], and the resilience benefits rest partly on anecdote and ongoing research [3][4]. Treat the weekly dose as a starting point, not a guarantee.

Health caveat. Huberman opens his episode by advising people to consult a physician before starting [2]. If you have heart or blood pressure issues, lung problems, Raynaud's or another medical condition, get a professional's advice before trying cold immersion or breathwork.

What To Do With It

1. Set a weekly floor of about 11 minutes, split into short bouts. Spread it over two to four sessions of a few minutes each, across two to three days, rather than one long session [1][2]. Huberman's own routine is about three sessions a week of two to six minutes [2].

2. Calibrate by feel, not by thermometer. Aim for the point where you want out but can safely stay [2], uncomfortable but not panicked [5]. Søberg notes that 12°C water, or even 19°C air, can activate brown fat, so you don't need ice [1]. If you're new, start cautiously, with cold showers for example [1].

3. Choose a number of walls before you get in. Decide in advance to climb three or five walls, meaning surges of "I don't want to do this," and change that number from day to day so the stressor stays unpredictable [2]. If you prefer something objective, log time and temperature like sets and reps, and expect to switch methods once you hit the ceiling [2].

4. Practice top-down calm while you're in. Use double inhales through the nose and long exhales through the mouth to settle, or deliberately lean in and grind [2]. Do mental work in the water, such as arithmetic, full sentences or recalling hard material, to train your cortex to stay online [2]. Move your limbs, with hands and feet submerged, so a warm layer can't form [2].

5. Get in, get out, get back in, and end on cold. Short, repeated changes in temperature do more than one long soak [1]. To maximize the metabolic effect, finish cold and let your body rewarm on its own rather than going straight to a hot shower or sauna [1][2]. If you want more, alternate one to three minutes of cold with one to three minutes standing in the air, arms at your sides, until you shiver [2].

6. Pair cold with offline breathwork, kept away from water. On separate occasions, practice cyclic hyperventilation followed by breath holds to learn calm under an adrenaline surge [4]. Never do this near water [4].

7. Time it for alertness. Do cold in the morning or midday, when you're ready to be alert for the next one to six hours [2]. If you train for strength or hypertrophy, keep immersion about four hours after the session or on another day [2]. Huberman does his plunge fasted in the morning [1], and warns against doing it on a very full stomach [2].

8. Notice whether it transfers. Do what Adolphs did. Watch your reactions to everyday irritants, like a horn, a bad-news text or a queue, and see whether the spike is smaller [3][2]. Cold works alongside other regulation practices he uses: intervening early, a few minutes of silence before switching tasks, and building tolerance for long efforts [3].

9. Progress safely once it's easy. When 11 minutes rarely produces walls, lower the temperature, lengthen the time or add a session, one change at a time [2]. Stay inside the hormetic window rather than chasing 20 to 30 minute ice swims [1].

10. Respect the safety rules. Always go with others in open water, be cautious about dunking your head, keep your hands out or wear neoprene if your extremities hurt, watch children closely, and check with a physician first if you have a medical condition [1][2][4].

Sources

1. Dr. Susanna Søberg: How to Use Cold & Heat Exposure to Improve Your Health · Huberman Lab
2. Using Deliberate Cold Exposure for Health and Performance · Huberman Lab
3. Dr. Ralph Adolphs on the Neuroscience of Emotions and How to Regulate Them · Huberman Lab
4. Unlocking The Power of Your Mind with Neuroscientist Dr. Andrew Huberman · The School of Greatness
5. LIVE EVENT Q&A: Dr. Andrew Huberman Question & Answer in Los Angeles, CA · Huberman Lab