Summary
Epsom salt (magnesium sulfate) has been used in therapy baths for hundreds of years to relieve muscle soreness and promote general well-being.
Adding 4lb-6lb of pure magnesium sulfate to your Morozko ice bath will soften your ice and may provide your body with transdermal absorption that supplements your magnesium levels.
Use only pure magnesium sulfate, without oils, perfumes or additives, because these may impact your water treatment system.
Do not add sea salts or any chloride salts because they interact with ozone in unhealthy ways.
Epsom salt ice bath
In Midland TX, Kinsey Williams and his wife own a therapy center called Source Float & Wellness that offers sauna, ice bath, light therapy, massage therapy, and sensory deprivation salt water float tanks.
To keep his float tanks salty, Kinsey buys pure Epsom salt (magnesium sulfate) in enormous quantities, hundreds of pounds at a time. So it's only naturally that he would eventually ask me, "Is it OK to add Epsom salt to my Morozko?"
It's a really good question, given that most people want the benefits of the Epsom salt bath, but are concerned about the integrity of their metal tub and the water treatment system.
Morozko vs Cold Plunge
Unlike float tanks, and almost all the cold plunges currently on the market, Morozko uses a metal tub to ensure that the water inside provides the same benefits of grounding (earthing) that you get whenever you're swimming in Nature. Moreover, adding a little Epsom salt will only increase the conductivity of the water an enhance the grounding effect.
With pure Espom salt, you don't have to worry about metal corrosion of tub. All Morozko models are designed with magnesium sulfate in mind.
So it's fine to add Epsom Salt to your ice bath, and there are some really good reasons why I recommend you do.
The benefits of Epsom salt ice bath
Epsom salt was originally extracted from natural mineral waters in Epsom, England and made famous by the wealthy and powerful people who made it fashionable to bath in. The springs were so popular among the 18th century English royals that local entrepreneurs discovered they could concentrate the salt by boiling off the water and sell the resulting crystals for use back in the mansions and palaces occupied by the wealthy when they were not travelling to Epsom.
It turns out that the royals of antiquity may have been on to something.
Because magnesium is a micronutrient essential to long life, and difficult to obtain in an 18th century English diet, bathing in the Epsom baths may have helped extend quality and quality of life for those privileged enough to afford it.
Although they didn't know this back in the 1700's, high blood serum levels of magnesium have since been associated with reduced risk of cancer, and improved muscle quality. I've written about the benefits -- even the necessity -- of magnesium in several other articles:
Nonetheless, the extent to which magnesium can be absorbed through the skin during an ice bath is difficult to assess. There are no studies that have attempted to measure dermal absorption of magnesium at the freezing temperatures typical of the Morozko. Moreover, the duration of the typical cold plunge is much shorter than the warm bath times that have been studied.
Under the most favorable conditions -- warm temperatures to open pores and long exposure times in the bath, some authors have concluded that magnesium will not enter the body through the skin (e.g., Gröber et al. 2017). However, any study that is based on measurements of magnesium in the blood is unreliable, because only 1% of the total body burden of magnesium is stored there.
The most extensive resource on transdermal magnesium therapies is by Dr. Marc Sircus (2011), who suggests that there are many factors that effect how much of anything is absorbed through the skin, including: the concentration applied, the length of contact time, and the total surface area of the body in contact. He never mentions temperature, and the possibility that cold might close up sweat glands and slow absorption, but it seems a reasonable supposition.
One way to increase magnesium absorption from your Epsom salt ice bath may be to keep the salt water on your skin during rewarming, and after. That is, don't shower after your ice bath. Towel off instead, rewarm, and leave the salt on your skin for extended absorption throughout the rest of your day, when your sweat glands reopen as you warm.
Adding salt lowers the freezing point of water.
Fresh water freezes at 32F (zero degrees Celsius), which is why your Forge water cannot cause frostbite. Ordinarily, bathing in ice water isn't cold enough to cause your skin to freeze, and that's one of the big advantages of ice baths over cryotherapy for those practicing deliberate cold exposure.
On other hand, seawater doesn't freeze until about 30F, because the salt ions in the water interfere with formation of ice crystals. The colder freezing point of seawater makes frostbite a possibility.
How much Epsom salt to add to an ice bath?
To approximate the concentration of salt in seawater, you'd have to add about 20lbs (9kg) of Epsom salt to a 6ft tub -- way more than is practical.
In theory, adding Epsom salt to your Forge could reduce the minimum water temperature, increase thermal discomfort, accelerate hormesis, and also introduce risk of frostbite.
In practice, the amounts of Epsom that you're likely to add to your Forge aren't anywhere near enough to have a measurable effect.
To turn your Morozko into an Espom salt ice bath, add 4-6lb of pure magnesium sulfate.
Don't use salts that have additives like essential oils or perfumes. The water treatment system will identify these as contaminants, and the ozone disinfection system will attempt to remove them. Under ozone attack, oils typically go through a partial oxidation phase in which they foam and can clog your filter.
You can find pure Epsom salt in 5lb bags online, or at most garden stores where it is sold as fertilizer. Just pour the salt into your tub and allow the water filtration to flow over the salt crystals until they are dissolved. It might take a few hours.
NOTE: Don't worry if your water turns green overnight. Magnesium is an essential micronutrient for algae, so when you first pour it into you ice bath, it can promote what is called an algal bloom. Swimming pool owners are probably familiar with waking up to the realization that they've neglected their chlorine dose when they see their pool has turned green overnight.
In swimming pools, the remedy for an algal bloom is chlorine shock, but in a Morozko we never use chlorine. Instead, let the ozone do the work. It takes about 24hrs of constant ozonation to destroy all the algae and return your water to a pristine, crystal-clear state.
How is it OK to add Epsom Salt to a metal tub?
The chemical name for Epsom salt is magnesium sulfate. It's different from table salt (sodium or potassium chloride), or road salt (calcium chloride), in one very important respect:
Epsom salt does not contain chlorine, or chloride.
The corrosive power of salt doesn't come from the positively charged ions, like sodium, potassium, iron, or magnesium. It mostly comes from the negatively charged ions, like chlorine. In Epsom salt, the negative ion is sulfate, not chlorine, and the corrosive power of sulfate is much, much less than that of chlorine.
So adding pure sulfate salts to your ice bath is not harmful to the metal, or to your skin, and it won't harm the water treatment and ozone disinfection system.. Just don't add chlorine salts. That means no sea salts, no Himalayan salts, and no table salts
The chlorine-ozone connection
Morozko ice baths are equipped with ozone disinfection systems to reduce the frequency of water changes and keep your water free of pathogenic microorganisms that might cause or spread disease.
We do not add chlorine disinfection to the Morozko because chlorinated water isn't safe.
Ozone is a more powerful oxidant than chlorine, but it is so reactive that it doesn't last very long. Except for the ozone contact chamber inside the mechanical space of the Morozko, actual ozone concentrations in the water are low, and measurements in the air above the ice bath consistently show near zero readings well below the EPA standard for ozone air exposures.
However, chloride ions accelerate the decomposition of ozone into oxygen, thereby deactivating the disinfection power of ozone. It is this reaction between chlorine and ozone that caused destruction of the stratospheric ozone layer above Antarctica, the emergence of the ozone hole, and the subsequent prohibition on manufacture of chlorinated hydrocarbons.
Adding chloride salts to your Morozko ice bath will undermine the efficacy of the ozone disinfection system designed to keep your water safe and crystal clear.
For salt water cold plunging, use only Epsom salt.
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.