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Don't Cold Overdose: Hypothermia, Frost Bite, & Brain Fog

Updated: Jan 23

How to recover from too much ice bath


  • There are several adverse effects of overdosing your deliberate cold exposure, including: hypothermia, frostbite, and brain fog.

  • In healthy bodies, rewarming reverses ill effects -- except for frostbite.

  • Use these precautions to minimize your risks of ice bath overdose, and still get your ice bath benefits.

Ice bath overdose?

I got a call from my friend Micah Lowe, founder of the ozone-at-home company Simply O3.

Micah is an advanced biohacker. He's in great shape, he keeps up with the science, and he has an extraordinary curiosity that motivates him to experiment with his limits.

This is what he said:

Thomas, I think I finally overdid it. Winter is almost here. It's about 34F outside now. So I did six minutes in my ice bath, then I did my recovery workout outdoors in the cold while I was still wet. That was a lot of cold, and I felt some brain fog after. I rewarmed with my Sauna Space lamps, went down for about an hour nap, and then I felt great. But maybe I did too much? - Micah Lowe, Simply 03

His experience raises some questions about what can happen when we overdose on deliberate cold exposure.

Ice bath safety

To get the benefits of deliberate cold exposure without risking adverse effects, there are some precautionary measures that are prudent to adopt in your practice.

Ice bath safety is a subject I've touched on in Getting Started with Cold Therapy and Dangers of Deliberate Cold Exposure. I listed three principal dangers:

  • drowning,

  • hypothermia,

  • heart attack.

But only one of those (hypothermia) relates to the dangers of overdosing on deliberate cold exposure. As I wrote in How much should you ice bath?, your cold dose depends on your cold acclimation. The more brown fat you've recruited from your past cold practice, the more comfortable you will feel in the ice bath without shivering.

Non-shivering cold thermogenesis

Most cells in the human body have hundreds of mitochondria to perform energy conversion, but brown fat cells are packed with thousands, because the most important function of brown fat is to fuel non-shivering cold thermogenesis. That's the mitochondrial process that oxidizes glucose and free fatty acids for the production of heat. The more cold exposure you get, the more your body will adapt by increasing brown fat depots (and 'beiging' white fat by adding more mitochondria). More brown fat means more non-shivering cold thermogenesis, thus more heat production, and greater comfort at lower temperatures.

One way to receive all the benefits of ice baths is to discover your personal minimum effective dose. For example, a study in Denmark discovered that an average of 11 min a week of winter swimming was sufficient to activate non-shivering cold thermogenesis in brown fat (Søberg et al. 2021). The study didn't explore the minimum effective dose, so it's possible that fewer than 11 min/week at water temperatures less than 40F could be sufficient. But the study did conclude that it didn't matter whether you did all 11 min at once, or spread it out over several days. That is, frequent, microdose exposures seemed to be as effective as less frequent, longer plunges.

Neither did the Danish study explore the maximum tolerable dose. In the extreme, hypothermia can result in heart stoppage. But when I asked an emergency room physician about cold water drowning victims, she cautioned me "A cold water case isn't dead just because they don't have a heartbeat. We always attempt rewarming and resuscitation. I've brought people back to life, so to speak, as much as 24hrs after they appeared dead."

In one extreme case, a 52-year-old Italian mountaineer was trapped in a crevasse for seven hours. His core temperature dropped to 79F, almost twenty degrees Fahrenheit below normal. Upon rescue, he suffered a heart attack. After six hours of continuous cardiopulmonary resuscitation and rewarming to nearly 97F, his heart began beating regularly on its own. He spent seven weeks recovering in the hospital and was discharged after a complete neurological recovery (Kuhnke et al. 2009).

Brain Fog

The brain is the most demanding single metabolic organ in the body, using more than 20% of all energy. During extreme cold exposure, so much energy is going into cold thermogenesis that the energy available for cognitive functions may be diminished. As I wrote in Cognition & Cold Exposure, this energetic brain drain might explain why I suffer deficits in working memory and mathematical reasoning when I'm in my ice bath.

Animal studies have revealed physiological changes in the brain during acute cold exposure that may explain the brain fog Micah experienced. As I wrote in Brown Fat for Brain Health:

Even small reductions in body temperature (mild hypothermia) have been shown to promote the phosphorylation of tau proteins in the brain, and tau phosphorylation is another of the signature physiological markers of Alzheimer's. In laboratory studies, chronic cold exposure induces tau phosphorylation and impairs memory and learning in rats - Ahmadian-Attar et al. 2014

In healthy subjects, cold-induced tau phosphorylation reverses upon rewarming. However, in subjects with compromised rewarming capacity, the resulting tangle formations can become permanent.

That doesn't mean the ice bath is making me stupid. In fact, the opposite is true.

For several reasons, keeping your brown fat active with a regular practice of cold exposure (and recovery) contributes to the long-term health of your brain. For example, when brown fat is activated by acute cold exposure, it produces a neuroprotective hormone called FGF21 that may contribute to long-term brain health (Tournissac et al. 2019). FGF21 has been shown to reverse cognitive deficits in rats, correct blood-brain barrier disruptions, protect against neurotoxicity, curb alcohol consumption in monkeys, and extend life in mice.

Healing brain trauma

Ice baths have even been used to speed healing from traumatic brain injury. Data from studies in rats suggests that cold water exposure promotes proliferation of endothelial progenitor cells that improve blood circulation in the brain and ameliorate cognitive deficits (Zhou et al (2017).

The subjective experiences reported by two friends are consistent with those findings. For example, Hollywood stuntman Chris Balualua sustained over 40 traumatic blows to the head during rehearsal and filming of a fight sequence for a major, big-budget movie. His brain injuries were so extensive that he couldn't sleep at all for 300 straight days. Cases like his are so rare that most doctors don't believe Chris could survive under such sleep-deprived conditions. Nonetheless, it also happened to Hungarian soldier Paul Kern, who did not sleep for four decades after being shot in the head.

Because Chris is a filmmaker he's documented many of his sleepless nights. When he came to visit, he had no experience with deliberate cold exposure. He spent five minutes in the ice bath -- most of it shivering uncontrollably. He rewarmed in the sunshine outside our studio in Phoenix AZ and reported to me later that he felt sharper, smarter, and had more mental stamina the rest of his day.

Chris has done two more sessions since then, and he reports that he has better word recall, is more fluent in conversations, and feels mentally quicker every time.

By some lucky coincidence, the same week Chris experienced his first ice bath, I met again with Justin Hoagland. Although I knew Justin had been deployed in Mosul, Iraq as a Navy SEAL, when he began suffered symptoms of multiple sclerosis, what I didn't know is that he also suffered traumatic brain injury. Justin's injury was caused by blast waves, rather than blunt force. As Dr. Kirk Parsley, the Sleep Doctor and himself a former Navy SEAL, explained it to us, when the shock waves from a powerful blast travel through the brain, they cause differential displacement of sections with different densities. The effect is to tear the brain apart from the inside, meaning that the damage is very difficult to detect on a scan. Like Chris, Justin reports that his ice bath practice helps improve his cognitive function, and has been critical to his long-term brain recovery, for both his brain injury and his multiple sclerosis. Which leads me to believe that there is more to the mental benefits of ice baths than just management of anxiety and correction of mood disorders like major depression.

Frostnip and frostbite

Some of our more adventurous engineers at Morozko Forge read about the how Epsom salts make ice baths better and they got a little carried away. After adding 18lb of Epsom salt (which is fine) to the ice bath at our Studio, they dropped the temperature setting down to 31F. Because salt reduces the temperature at which water freezes, with that much salt in the water, dropping the temperature setting changed the ice bath into a 20" deep tub of icy slush.

They did seven minutes each.

Two days later I got a call from one of them, asking me about painful skin, all over his body. He said it felt like a painful sunburn, but he felt it almost everywhere, and he hadn't been out in the sun.

I was flummoxed.

So I asked him, "What about your plunge buddy? Does he feel the same?"

He did.

It turns out they had given themselves frostnip. As I wrote in Cryotherapy vs. Ice Bath, one of the dangers of sub-freezing temperatures is that they can freeze the water inside your skin cells, which is called frostbite.

Frostnip is pre-frostbite. It is painful, but reversible. Although Wim Hof healed a frostbitten toe with the focused power of his mind, for those of us without such complete control of our metabolism, frostbite can cause permanent damage. When our engineers dropped the temperature of their ice bath below freezing, they introduced the risk of freezing their own skin.

And they both recovered in a couple more days.

Precautionary Protocols

It's no surprise that Micah experienced a full recovery after rewarming and nap, but how can he avoid cold overdosing in the future?

Keep your cold exposure above freezing

When Micah emerged from his Morozko and commenced his recovery workout in the cold winter air without drying off, he increased his cold dose in two ways: 1) cold air exposure, and 2) heat extraction by evaporation.

As the water dried off his skin, if carried more heat with it, further cooling his skin. Had the outdoor temperatures been below freezing, he would've risked freezing the water right off his wet skin and leaving behind frostnip or frostbite. As it was, the air temperatures were above freezing, so he wasn't risking frostbite -- he was just slowing down his rewarming process by increasing his cold dose.

Our first precautionary practice is to keep your ice bath above freezing and dry off before exposure to freezing cold air.


What Micah did well was to seek rewarming after his workout with his sauna lamp. Red light and near-infrared light (NIR) exposure will boost the mitochondrial function in your skin, to accelerate your recovery.

Although some scientists advise to allow your body to rewarm naturally, even if you feel chilly for hours after your deliberate cold exposure, that advice doesn't help with cold overdose. In case you've overdone it, rewarming with sauna is good advice.

But what if you haven't got a sauna?

At the end of my video lecture in Stress vs Cold I introduced you to a 9-year old girl with cerebral palsy (CP) who did 4 minutes in the ice bath, and inspired her mother with Raynaud's syndrome to ice bath as well.

That little girl is 12 years old now, and she still gets relief in the ice bath. When she saw Joe Rogan do 20 minutes in his Morozko ice bath, she decided she wanted to do more than Joe.

She was in a 34F ice bath for 30 minutes before her mother pulled her out, which is to say she overdid it.

When she emerged, the combination of her cold exposure and her CP meant she barely had motor control of her legs.

Without a sauna to facilitate her rewarming, her mother was understandably concerned. So we invented something I now call the "car sauna."

I said, "Get into your car, blast the heat as high as you can stand it, and park it in the sunshine until she rewarms."

In Phoenix Arizona in the summer, the sun alone can raise the temperature of a car to over 160F -- plenty warm enough to constitute a sauna experience. Even if you don't live in Phoenix, if you find that you've overdosed your cold exposure and you don't have a sauna, or sauna lamps, or a wood stove, you probably at least have access to a warm car.

Our second precautionary practice is to pursue active rewarming, through exercise and warm, dry air.

The two caveats to the car sauna idea is that when I've tried it without cold exposure beforehand, I find that sweat from my brow can enter my eyes and temporarily blind me. And when I'm experiencing afterdrop following my ice bath, I'm not in any shape to drive. Because driving a car is dangerous, and you shouldn't do it while you are impaired in any way, the safest way to do car sauna is to keep your car parked in a safe place while you (or your passenger) rewarms.

These two precautions will help you recovery faster when you overdo it a little, like Micah did.


About the Author

Thomas P Seager, PhD is an Associate Professor in the School of Sustainable Engineering at Arizona State University. Seager co-founded the Morozko Forge ice bath company and is an expert in the use of ice baths for building metabolic and psychological resilience.

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