Updated: Apr 12
"Is it OK to add Epsom salt to my Forge?" a new customer asked the other day.
It's a really good question, given that most people understand salt will accelerate metal corrosion and the galvanized metal tubs in the Cold and Filtered Forges won't last forever. (The Stainless Forge is chemically indestructible under all practical bathing conditions).
But the answer regrading Epsom salt might surprise you.
Yes, it's fine to add Epsom Salt to your ice bath, and there are some really good reasons why you might want to.
Espom salts are safe and fun for your Forge, and may have health benefits by supplementing your magnesium levels, but chloride salts (e.g., table salt, road salt) are not safe and not fun.
How is it OK to add Epsom Salt to a galvanized metal Forge?
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.
The corrosive power of salt doesn't come from the positively charged ions, like sodium, potassium, iron, or magnesium. It 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 sulfate salts to your Forge water is not harmful to the metal, or to your skin. Just don't add chlorine salts, or you risk dissolving away the galvanized coating on your tub -- literally eating away your investment in your Forge.
What are the benefits of cold plunging in Epsom Saltwater?
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.
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 Forge. 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 -- the best studies indicate that magnesium does not enter the body through the skin.
That means the experience of Epsom salt cold plunging is more aesthetic than medicinal.
Except for ...
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.
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.
One more thing about chlorine salts -- the ozone connection
Filtered and Stainless Forges 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 Forge 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, Outside the ozone contact chamber inside the mechanical space, actual ozone concentrations in the Forge water are low.
Nonetheless, 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 Filtered or Stainless Forge will undermine the efficacy of the ozone disinfection system designed to keep your water sa