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Ice Bath Science: Facts, Myths, and Mysteries

Updated: Jan 23

Knowledge comes from both systematic investigation and individual experience

Thomas P Seager, PhD sitting on a window ledge with a mobile phone pressed against his ear.
In my experience, the only scientists who wear white lab coats are the ones you see on TV. I'm a scientist, and most of the time, I look like this.

There has been an explosion of biohacking articles available online that repeat the same claims about ice baths, cold showers, cold plunges, cold tubs, and deliberate cold exposure. Most of them say the same exact thing, because they are all copying from each other in a competition for higher Google search rankings.

There are two things absent from these search-engine optimized articles with click-bait headlines: 1) true stories of what has worked for others, and 2) real scientists.

The advantage of personal stories is that they are rich in context, and inspiring to others. The disadvantage is that they are viewed as anecdotal, and rather than being accepted as helpful for generating new scientific hypothesis, too many people with college-level educations will often complain "Well, there's no proof in anecdote."

Science is about knowledge (not prestige)

I spent more than six years in graduate school earning my Ph.D. in environmental engineering. I have published over 100 scientific studies in peer-reviewed journal articles, dozens more book chapters, and I've won millions in research grants from the National Science Foundation, the Environmental Protection Agency, and the US military. I'm a tenured faculty member at Arizona State University, and near the top of my profession.

And I would never deny the knowledge of an individual's experience, because people do not need scientific "proof" to describe what has happened to them.

The advantage of science is that it is generally true, rather than true for just one person. Medical studies most often search for statistical likelihood, because it suggests that what was true for a large group may also be true for an individual.

But it might not.

How Adrienne cured her Hashimoto's thyroiditis

For example, when Adrienne reversed her Hashimoto's thyroiditis, allopathic medical professionals had already told her that reversal was impossible, because the general understanding of thyroiditis is that it is chronic, progressive, and life-long.

Curing Hashimoto's disease by practicing daily ice baths transformed a sick, obese woman into her lean, beautiful former self.
Morozko Forge co-Founder Adrienne Jezick stabilized her thyroid function and corrected her metabolic disorders by adopting a practice of regular deliberate cold exposure in her ice bath.

Yet, there can be no denying Adrienne's experience with reversal, and the laboratory testing that demonstrates she is free of her previous disease. In the simplest sense, Adrienne is cured.

So the next question is, "What does science say that might explain the mechanisms of Adrienne's cure?"

Had we denied her individual experience as anecdotal, or lacking in proof, we might not have troubled to research what sort of scientific knowledge is available that supports her experience.

As it turns out, the thyroid controls metabolism, so it makes sense that Adrienne's metabolism was dysregulated while her thyroid was malfunctioning. It was her thyroid disorder that caused her to become obese and sick.

But what regulates the thyroid?

The answer is brown fat.

Science of cold thermogenesis

There are at least two types of fat in the mammalian body. It is white fat that stores energy, and is characteristic of obesity. The vast majority of our fat cells are white fat.

Brown fat exists only in small quantities, around the clavicles, between the shoulder blades and around the heart. Brown fat cells are packed with mitochondria, and their sole responsibility within the body is to produce heat during cold exposure, so that the body can maintain temperature using a process that Ben Greenfield calls cold thermogenesis.

Until a little over a decade ago, brown fat was undetectable in conventional medical scanning, so doctors thought that it only existed in human children as "baby fat." In the opinion of medical science, adults outgrew their brown fat. However, about ten years ago a new type of PET scan revealed brown fat in some adult human subjects, and doctors changed their views.

Since then, there has been an explosion of new research related to brown fat, and one of the most important findings is that more brown fat correlates with more thyroid stimulating hormone in the blood stream. In other words, the thyroid regulates metabolism, and brown fat regulates the thyroid.

Because Adrienne grew up in Florida, lived in Arizona for years, and reportedly hated the cold, it makes sense that she lost nearly all her brown fat. Adults will not retain brown fat in the absence of cold exposure. Thus, when Adrienne began her ice bath practice, she recruited new brown fat, stabilized her thyroid, and fixed her metabolism.

Ice Bath Science

Adrienne's example describes how the individual experience and the general science can combine to create a powerful story rich with knowledge that may help other people. I've spent over three years gathering individual stories of miraculous health recoveries that defy allopathic medical norms, and investigating the scientific studies that might explain the mechanisms and perfect our understanding of the phenomena. The result has been a synthesis of individual experience with generalizable science that allows me to sort many of the popular claims about ice baths into three categories:

  1. FACTS,

  2. MYTHS, and


This article reviews what I've discovered, using knowledge from both science and experience, so you can decide for yourself what sort of deliberate cold exposure practice might work for you. It's written in a question & answer format, so you can browse for the information that speaks to your health goals, and skip the rest. I'll update it from time-to-time, because we are still accumulating new knowledge and we always will.

Can ice baths correct thyroid disorders?

Adrienne's experience is not unique, or isolated. For example, Dr. Courtney Hunt has also corrected her own thyroid using ketosis, fasting, sunlight, and supplements that support metabolic health. And Dr. Hunt is a big advocate for deliberate cold exposure, prescribing it for many of her patients.

The fact that thyroid disorders, including Hashimoto's thyroiditis, are reversible is a FACT that allopathic medicine has overlooked. While Adrienne did not use ice baths alone, the essential role of brown fat in modulating thyroid function means that just enough cold exposure to stimulate shivering will speed your recovery.

Can ice baths cure cancer?

One of the most controversial public health policy issues is the extraordinarily poor progress that has been made since Nixon declared a "war on cancer" in 1971 (e.g., Hanahan 2014). While progress has been made in treating specific types of cancer, such as Hodgkin's disease, overall progress in extending lifespan in cancer patients has been miniscule. The last two decades of new drugs have extended average life expectancy of cancer patients by less than four months (Feldman 2019).

Dean Hall is an exception.

As with Adrienne, his experience raised questions in my mind about the scientific mechanisms that might explain Dean's miracle. What I discovered is that 50 years of research at the National Cancer Institute has been spent looking in the wrong place.

According to Thomas Seyfried Ph.D., cancer is primarily a metabolic disease (Seyfried 2012). Most cancer cells rely on glucose to fuel their rapid growth, which suggests that avoiding high blood sugars will help starve cancer cells. Seyfried has documented case studies in which a low-carbohydrate, ketogenic diet will slow tumor growth -- without allopathic chemotherapy (Seyfried 2021). And his results agree with a recent review of the ketogenic diet as adjunctive therapy for cancer agrees (Weber et al. 2020).

Given that an ice bath is the fastest way to generate endogenous ketones, it makes sense that ice baths could contribute to recovery from cancer. In Dean's case, his intense cold water swimming regimen must have put him deep into ketosis, given that he reports his supervising medical doctor expressed concern for his extreme loss of body fat during his swim.

In Dean's case, his weight loss wasn't because he was getting sicker. It was symptomatic of his journey towards metabolic health.

Nonetheless, there are no systematic scientific studies that test ice baths or deliberate cold exposure for tumor management in isolation. While the evidence suggests that ice baths, fasting, and exercise in combination support cancer treatments, whether some form of deliberate cold exposure can cure cancer remains a scientific MYSTERY.

Can ice baths cure depression?

I got an email from a delighted customer a few days ago, who said:

I can't tell you how much I love my Forge. Because of your cold plunge, I am now off the anti-depressants I took for six years.

He's not alone.

AnnaLynne McCord, who revealed in 2021 that she has been diagnosed by brain specialist Dr. Daniel Amen with dissociative identity disorder, claims that her ice bath practice helps her manage anxiety and makes her feel "HIGH AF 😂😂😂."

That may be why another movie star customer refers to his Forge as "the mood changer" -- because whole body cold water immersion initiates a complex cascade of neurotransmitter production, the most powerful of which is a 3x dopamine boost associated with cold water therapy (Šrámek et al. 2000).

My own experience confirms the power of the Forge to help me manage stress and anxiety.

While it seems counter-intuitive, brain wave data we collected using the Muse headset shows that whole body cold water immersion induces a reliable meditative state. That is, the ice bath is a meditation for people who haven't trained to meditate, and this may contribute to the mental health benefits of the ice bath.

What little science is available confirms that cold water swimming can be an antidote to mood disorders. As a treatment for depression, anxiety, low mood, and stress management, ice bath therapy is FACT.

Can ice baths reverse Type 2 diabetes?

Deliberate cold exposure provides many of the same metabolic benefits as exercise, but faster. At near freezing temperatures, a few minutes in the ice bath can provide a metabolic boost that lasts for hours.

This is an area in which the science is ahead of our personal experience. For example, one study of obese, late middle-aged German men showed reversal of Type 2 diabetes after only ten days of mild cold exposure -- without exercise or changes in diet.

If that's the case, then we should be able to observe improvements in markers of diabetes among our customers base, right?

In fact, we have several Forge customers who report blood glucose improvements as a result of their ice bath practice.

Wade Hogg is one of them. He sent us continuous blood glucose monitoring data that showed an immediate drop resulting from whole body cold water immersion.

What's more, he reported that this effect lasted for hours after he completed his ice bath.

While the persistence of these effects remains uncertain, use of ice baths to improve insulin sensitivity and reverse Type 2 diabetes is a FACT.

Can ice baths help you lose weight? Boost testosterone?

Any number of scientific studies have demonstrated that activation of brown fat from deliberate cold exposure will elevate metabolism and burn fat. However, the effective use of ice baths to lose weight, or make lasting changes in body composition, has yet to advance beyond the hypothetical.

That may be because there is no documented case of anyone who has "ice bathed" their way to dramatic weight loss. I wrote about my own case in 'Calories & Cold Exposure' and concluded that ice baths alone as a strategy for weight loss is a MYTH. For example, a recent study in mice suggested that compensatory metabolic mechanisms (e.g., lower body temperature and metabolism during sleep) resulted in reductions in energy expenditure that made up for the increased metabolism and fat burning during and following intermittent cold exposure (Ravussin et al. 2014).

Your best bet for improving your body composition is to improve your diet and add some weight training. Nonetheless, a regular ice bath practice will correct metabolic disorders, and when used prior to exercise, it will boost your testosterone. Those hormonal benefits alone will likely help trim visceral fat, build muscle, boost your energy levels, libido, sexual activity, and improve your body image.

I discovered this quite by accident.

I had been using fasting and ice baths to help me generate ketones because blood tests showed elevated levels of prostate specific antigen (PSA) in my blood stream, which meant I could be at elevated risk for prostate cancer. I had spoken with other men who had biopsies or prostate removal surgery, and I was determined to explore alternatives. I only began a program of exercising after my ice bath because it helped me rewarm.

When I retested my blood for PSA, I also tested for testosterone. It turns out that my PSA went down to 0.8 ng/ml (low risk) and my testosterone jumped to 1180 ng/dL, which would be a good reading for man a less than half my age. My urologist ordered me tested for a testosterone precursor called luteinizing hormone (LH), just to be sure I wasn't using steroids, and I tested off-the-charts for LH, too!

It could have been some sort of coincidence, except that my results corroborated a 1991 Japanese study that showed exercising after an ice bath will do exactly what was happening to me -- increase my T levels. Moreover, a study of Italian rugby players demonstrated that one week of twice-a-day whole body cryotherapy (morning before workouts, and evenings after) resulted reliable increases in testosterone in athletic young men who already had high levels (Grasso et al. 2014).

If these results, my experience and the two studies, are i, then we ought to be able to replicate them in other men, right? That's exactly what happened to Jason. He started testing his testosterone levels and discovered that he went from the mid-500's up to 913 ng/dL in two years.

The positive effect that ice baths before your exercise can have on your testosterone levels is a FACT.

Can ice baths cure allergies?

I got an email from an customer who is avid about both their Forge and testing/tracking their health improvements. They got a pleasant surprise from his allergist a few months ago, and I'm going to share the email here in its entirety.

I had suffered from allergies which started 10 plus years ago. I didn't get tested until March 12, 2018. On that date I had a skin prick test which showed positive for four allergies: mite DF, mite DP, ash, and cockroach. By far the dust mites were the allergies that caused me significant problems. On December 22, 2021 (after six months using my Forge) I went back to the allergist and had updated skin prick testing done. The test showed that all allergies had resolved. The doctor was surprised, so at the same visit he also did a blood draw to specifically test for dust mites, since that was the allergy that caused me the significant issues in the past. The IgE blood test also showed negative. The doctor's response was just to throw up his hands and say "sometimes they resolve." I'm not sure if that is helpful, but I keep a pretty close track of my health in terms of daily tracking of activity, sleep, nutrition, supplements, exercise, etc. and the only major change I had made in the several months prior to my negative test results was my Forge deliberate cold exposure.

One good customer story is a hypothesis, not a statistical likelihood. But Adrienne and I got to talking about how ice baths helped Kara Dunn managed her Guillain-Barre syndrome (pictured). Like allergies, GB is an auto-immune disorder. On Dr Hunt's recommendation, Dunn incorporated ice baths into her successful recovery from GB. So, if ice baths can help with GB, might they also help with allergies?

We don't know for sure, and that means whether ice baths can cure allergies remains a MYSTERY.

But Adrienne reports that, after decades being unable to eat eggs, she isn't allergic to them anymore.

Can ice baths boost fertility?

We've already established the healthy effects on testosterone that ice baths followed by exercise can have for men, and it is well documented that higher T-levels are correlated with increased male virility.

But what about women?

Dr. Courtney Hunt reports that many of her female patients who follow her prescriptions regarding sunlight, nutrition, ketosis, and cold exposure become pregnant -- even in their 40's. Her experience is supported by stories our customers tell us about conceiving shortly after receiving their Forge, and it is corroborated by Josephine Worseck, Ph.D., who has chronicled her ice bath pregnancy and post partum recovery on Instagram.

I first wrote about Worseck in 'Cold Plunge During Pregnancy' in which we cited several studies establishing that deliberate cold exposure is healthy and beneficial for pregnant women. Since then, I've chronicled Marisa Lopez' experience during her first pregnancy, and the success she had using ice baths to manage stress and anxiety, while ensuring her metabolic health. In those articles, I cite several studies from around the world showing seasonal patterns suggesting heat can be detrimental to pregnancy and cold exposure beneficial, according to Worseck, whether ice baths will aid in conception remains a scientific MYSTERY.

All she can say for right now is that they worked for her.

Can ice baths cure multiple sclerosis?

Two of our earliest customers bought their Forge because they know that ice baths are the best way for them to manage their multiple sclerosis (MS).

For example, Justin Hoagland is a former Navy SEAL who was diagnosed with multiple sclerosis while deployed in Mosul, Iraq. His condition was so severe, and so rapid in its onset, that he was reduced to a wheelchair at different periods in his life when he experienced particularly acute flare ups.

Since commencing his ice bath practice, he has recovered to such a remarkable extent that he now he posts workout videos on his Instagram.

Our other customer with MS is also an athlete. Julie Blew is teaches yoga and sometimes uses her Forge three times a day during the summer to help manage the symptoms of her MS. She has been so successful in her cold therapy that she's been able to resume running 10K races. She's even written a memoir about it titled Like the Wind... Not the Color (Blew 2021)

While we have both experiential and scientific evidence that recommends ice baths for managing symptoms of multiple sclerosis better than drugs, it is improper to suggest that ice baths can cure MS. While both Justin and Julie are remarkable cases, ice baths will not reverse the damage done to their nervous systems, and the mechanisms by which cold exposure gives them the relief they experience remains a MYSTERY.

Can ice baths improve heart rate variability (HRV)?

Hausswirth et al. (2013) measured the cardiovascular effects of partial and whole-body cryotherapy, compared to a control group. They discovered that, although blood pressure rose in response to cryostimulation, other heart measures related to mood improved. Namely:

  1. pulse went down (HR, below), and

  2. HRV went up (as measured by root mean square standard deviation, RMSDD & high frequency band, HF).

Whole body cryotherapy improves heart rate variability
Whole body cryotherapy improves cardio-vascular markers of health.

Moreover, whole-body cryostimulation induced stronger effects than partial body.

Most people don't know that Heart Rate Variability (HRV) is one of the most important physiological markers of mental health.

Reduced HRV has important functional significance for motivation to engage social situations, social approach behaviours, self-regulation and psychological flexibility in the face of stressors. Over the longer-term, reduced HRV leads to immune dysfunction and inflammation, cardiovascular disease and mortality, attributable to the downstream effects of a poorly functioning cholinergic anti-inflammatory reflex. -- Kemp & Quintana (2013).

Increasing HRV protects against low mood, depression, anxiety and stress. While we have yet to measure improved HRV in a new customer or subject undertaking a regular ice bath practice, the reliable dose-response relationship between cryotherapy and increased HRV reinforces adds evidence to the FACT that a regular ice bath practice will help relieve anxiety, stress, lift mood, and is likely to improve cardio-vascular health.

Can ice baths boost the immune system against infection?

It's ironic that we use the word "cold" to describe a typical coronavirus infection. It may be because cold and flu season come during winter, but viral infections are seasonal because of changes in sun exposure and the Vitamin D deficiency that results from the shorter days and lower sun angles of winter -- not because of colder outdoor temperatures. According to a study sponsored by the US Army, "there is no support for the concept that cold exposure depresses immune function" (Castellini et al. 2002).

Just the opposite may be true (Mooventhan & Nivethitha 2014).

A randomized study of healthy Dutch adults with no prior experience in cold exposure found that a daily regimen of cold showers reduced sick day absenteeism by 29% compared to a control group (Buijze et al. 2016). That doesn't by itself suggest that cold exposure boosts the immune system, because they might have had a myriad of reasons for feeling better and calling in sick less, but it supports the idea that cold exposure can contribute to overall health.

A more systematic study of cold exposure and the immune system concluded that "repeated cold water immersions... activated the immune system to a slight extent" (Jansky et al. 1996). Effects were measured over six weeks, during which participants underwent whole body cold water therapy for 1 hr at 14C (high 50's F), three times a week.

Most Morozko Forge customers experience shorter, colder, more frequent immersions, and the best investigation of that kind of practice was conducted in cooperation with Wim Hof. Over ten days, he taught his method of breathwork, meditation, and cold exposure to a group of health Dutch young men who were subsequently injected with Escherichia coli endotoxin to test their immune system response. Compared to controls, they found that the Wim Hof trained subjects "experienced fewer endotoxemia-associated flu-like symptoms, and a more swift normalization of fever and cortisol levels, which are likely the result of the attenuated proinflammatory response" (Kox et al. 2014).

These results reinforce popular claims that cold exposure provides a boost to the immune system as a FACT, but the effect does not appear so strong as to suggest that ice baths alone will prevent infection.

Can ice baths improve athletic performance?

While athletes have been using ice packs and ice baths at least since the invention of refrigeration, there remains considerable controversy over their benefits. There are three FACTS that are important to keep in mind, and I've described each of them here.

Cooling boosts performance. As exercise warms the human body, several mechanisms begin that will protect us from the dangers of hypertrophy (overheating).

  • The first is sweat, which cools the skin by evaporating water stored inside the body to the surrounding air. That's why humid air always feels warmer than dry air, because the rate of sweat evaporation is slower when the humidity is high.

  • The second is fatigue. As the body warms, fatigue makes further exercise more difficult, slowing the rate at which the body generate heat that must be removed from the body.

Thomas P Seager performs a leg press on the ARX Fitness machines after pre-cooling in the Morozko Forge ice bath.
Pre-cooling in the ice bath improves workout performance, as measured at ARX fitness in Austin TX.

We've probably all felt the refreshing boost of energy that comes from a cool breeze during a hot workout. Ten years ago, Stanford biologists confirmed our experience in an experiment that measured a 30% increased work output during the bench press, and nearly doubled during pull-ups, resulting from cooling the palms during a strenuous workout (Grahn et al 2012). Participants in that study spent 30-45 minutes warming on a treadmill, then performed palm cooling, then their measured exercises. In other words, their cooling happened in the middle of their workouts.

However, since we installed a Forge at ARX Fitness in Austin TX, we've observed that pre-cooling before a workout results in similar gains of 25% or more, as measured by the ARX constant displacement machines. The rationale remains the same -- i.e., starting at a lower skin temperature slows warming of the body during exercise, and postpones fatigue.

Whole body cold water immersion improves endurance in Navy divers.
Looney et al. (2019) found that diving endurance is improved when immersed in cooler water.

The opposite is also true.

US military researchers measured the core body temperature of Navy divers working in waters ranging from 34.4C to 38.6C (94F to 101.5F) -- in other words, slightly lower than and higher than typical body temperature of 37C (Looney et al. 2019).

Because the divers were immersed in water, evaporation of sweat was unavailable to them as a cooling mechanism. What's worse, these trained divers were using scuba gear to breathe, meaning that they could not use panting (as dogs do) to augment cooling.

Immersed in warm water, Navy divers exhibited only 20% of the endurance typical of cooler waters.

The phenomenon of increased athletic performance after cooling is a little known FACT.

Icing your muscles will speed recovery. Because cold therapy is so effective for reducing inflammation, it has long been used by athletes to relieve the pain of muscle soreness after strenuous exercise. Most athletes report that icing soon after a workout or a competition feels good and prepares them to return to strenuous exercise.

Scientific studies corroborate their experience (e.g., Lombardi et al. 2017). For example, a review of laboratory-controlled studies of whole body cryotherapy for exercise recovery found reduced pain, improved performance, and reduced markers of inflammation when cold was applied immediately following muscle-damaging exercise (Rose et al. 2017). The phenomenon of whole body cold exposure reducing soreness and speeding return to competition is a FACT.

Icing too soon after exercise will slow long-term anabolic gains

Studies of cold for exercise recovery are fraught with inconsistencies, methodological errors, and misinterpretations -- leaving athletes and coaches confused. What gets overlooked is that application of cold immediately after exercise will short-circuit longer-term anabolic gains, even as it speeds return to previous levels of performance. That is, post-exercise cold therapy improves short-term recovery at the expense of longer term gains (Kweicien & McHugh 2021). For example, one study found reduced muscles mass in subjects that practiced post-workout cold water immersion, compared to those who practiced active recovery using a stationary bike (Roberts et al. 2015).

For athletes seeking to maximize long-term gains during training, the advice to avoid cold exposure for at least two hours following a workout is based on FACT. Some researchers even suggest applying of heat immediately after training, to enhance gains (Cheng 2018).

Are ice baths dangerous?

Joe Rogan's ice bath video from his Forge last summer touched off a firestorm of critics questioning the safety of 20 continuous minutes of cold water cryotherapy.

So I wrote an extensive research piece detailing the dangers of the ice bath, and the behaviors that will reduce your risks.

The most dangerous thing Joe Rogan did the day of his 20 minute ice bath was drive to work afterwards.

The dangers of ice baths have been grossly exaggerated. For example, Kelly McGonigal, Ph.D. is a Stanford psychologist whom I've cited often regarding the hormetic (Kouda & Iki 2010) benefits of stress. However, when she wrote that immersing your whole body in 34F water "would kill you in less than a minute," she revealed that she has no idea what she's talking about in the area of deliberate cold exposure (Upside of Stress, McGonigal 2012, p186).

Nonetheless, some risks and dangers are inherent in every ice bath is a FACT, and there are at least at least important safety tips I recommend to ensure a safe practice:

  1. Forge sober,

  2. Supervise children,

  3. Always Forge feet first, and

  4. Breathe.

You might notice that none of these measures related to the risk of hypothermia, and it's because it would take more than an hour of ice bath exposure to induce a dangerous drop in core body temperatures. Rather, the first two measures are intended to minimize drowning accidents, while the last two address concerns about heart rate irregularities.

The difference between science, experience, and medical advice

There may be other conditions (such as very high blood pressure) that contraindicate for an ice bath practice. I recommend consulting with your medical professional for advice that is specific to you, because sometimes what works well for others will not be a good fit for your specific health condition.

Nothing in this article, or on our website, should be mistaken for medical advice. Remember that stories of experience describe what has been true for individuals, and may not generalize to others, while science typically describes statistical likelihoods and mechanisms that may not prove true for your individual circumstances.


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.For more information on taking charge of your own physical & mental health, visit the Self-Actual Engineering newsletter at

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