Summary
Both cold water immersion and cold air exposure are forms of cryotherapy.
All forms of cryotherapy work by activating the sympathetic nervous system via cold receptors -- primarily on the skin.
Cryotherapy extracts heat from the body, prompting cold thermogenesis.
Cold air has a lower coefficient of heat transfer than cold water. Therefore, cold air cryotherapy requires much colder temperatures to achieve the same rate of heat extraction.
Colder temperatures introduce a risk of frostbite in cold air cryotherapy that is not present during cold water immersion.
Some people prefer cold air because they don't want to get wet, or they do not want to share bath water with other people.
Cryotherapy or cold water immersion?
The use of deliberate cold exposure for promoting health and wellness is called cryotherapy. For example, when you use an ice pack to reduce swelling around an injury, that's cryotherapy. However, the use of cryotherapy for the whole body has become increasingly popular among extreme athletes, biohackers, and people seeking relief from chronic illness.
There are principally two approaches to whole body cryotherapy: 1) frigid air, and 2) cold water immersion. They both work by activating thermoreceptors on the skin to signal vasoconstriction and thermogenesis through the autonomic nervous system.
Cryotherapy extract heats from the body. The more heat extracted, the more metabolic work is required to maintain a constant body temperature.
Cold water is several times more effective for heat extraction than cold air, so to obtain the same amount of heat extraction in the same time as cold water, frigid air cryotherapy has to expose the body to much, much colder temperatures.
The most important distinction between frigid air cryotherapy versus cold water is the risk of frostbite.
For example, during the 2019 National Football League preseason, Antonio Brown (perhaps the most talented wide receiver at the time) was been held out of the Oakland (California) Raiders training practice because of frostbitten feet.
It's not unusual for athletes like Brown to use extreme cold air cryotherapy to speed recovery from strenuous exercise, boost the immune system, and reduce inflammation. Lebron James (National Basketball Association) is one of the most famous practitioners.
But frigid air cryotherapy temperatures are so cold that they can freeze the skin right off your body.
For Antonio Brown, that's exactly what happened.
The whole story inspired us to revisit Rhonda Patrick, PhD's authoritative review of cold exposure science. In her article 'Cold Shocking the Body' she compares frigid air cryotherapy and cold water immersion (i.e., ice bath cryotherapy).
According to Dr. Patrick, given a constant time of immersion, there are three important variables that govern the effectiveness of any cold exposure therapy. They are:
Thermal conductivity. How fast does the cold media absorb body heat?
Exposure. How much skin is in contact with the cold media?
Temperature gradient. How cold is the media?
Dr. Patrick writes, that for thermal conductivity "ice has the greatest capability to extract heat from the body, followed by cold water, and then air." While skin exposure can be controlled with all three media, it is the temperature gradient "where cryotherapy really shines, because the air temperature can be as low as -178°C. That is cold."
And we think that's a problem.
Cryotherapy uses liquid nitrogen to create temperatures that are so cold, they can freeze the water inside your skin cells, causing these cells to die, the skin to blister, and slough off from the body. That's what frostbite is -- the water inside the cells of your body freezing to ice.
To prevent frostbite, cold exposure practitioners are supposed to wear mittens, thick socks or booties, and a head band, mask, and googles (when the head and face are exposed) to protect ears, nose, eyes, and lips.
Antonio Brown wasn't wearing his booties, and that's how he froze the soles of his feet right off.
While we admire Brown for what must be an incredible tolerance for pain, we're not impressed with his results. Injury is the opposite of recovery.
One of the reasons we prefer ice bath cryotherapy is because the temperature of the fresh water in Morozko Forge can never fall below 0°C. Whenever there is water in the Forge, by definition the temperature is at or above freezing, so you can't get frostbite from fresh ice water.
Only frigid air cryotherapy, or sub-freezing ice packs, can give you frostbite. In this way, ice water is safer..
So why do cryotherapy centers use $100,000 liquid nitrogen machines instead of a $20,000 Morozko Forge?
Because cold air is perceived as more sanitary than cold water.
The notorious reputation of hot tubs as cesspools of pathogenic soup has contributed so much to the stigma of sharing a bath with strangers that wellness centers probably offer cryotherapy rather than cold water immersion to (ironically?) create the impression of safety.
That's why the Morozko Forge comes equipped with water treatment systems that use microfiltration and ozone to keep the Forge water safe and crystal-clear.
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 https://seagertp.substack.com/.