Are Epsom Salt Baths an Effective Treatment for Running Injuries?

A while back, I was dealing with a nagging foot injury and the veteran physical therapist I was working with recommended I try soaking my foot daily in a solution of warm water and Epsom salt.  This trick was, apparently, popular with top-level soccer players with foot injuries.

Though I eventually got over the injury, and did dutifully use Epsom salt soaks while doing so, I never figured out whether it really helped or not.  So today, we’ll look into whether there’s any research backing this old-school injury treatment trick.

What is Epsom salt?

“Epsom salt” is the common name for magnesium sulfate, a simple compound that’s sold in bulk packages at drug stores for gardening, use as a saline laxative, and as a “soaking aid” for injuries.

I’m not sure where using Epsom salt solutions to treat athletic injuries originated, but it does has a history of being used in creams and wraps applied to injured race horses (along with all sorts of essential oils and other dubious ingredients).

Regardless of its origins, however, Epsom salt soaks are not a particularly well-studied treatment.  In fact, there are no direct studies of the effectiveness of Epsom salt solutions when treating any kind of athletic injury, acute or chronic.

Theories

We could just end here and say there’s no scientific support for Epsom salt baths, but its popularity among old-school athletes, trainers, and physical therapists warrants some consideration—if Epsom salt baths did indeed have some effect on improving recovery or reducing pain from athletic injuries, what type of mechanisms could be responsible for this?

A combination of magnesium and sulfate ions

Even here, the scientific evidence is limited, but there are some theories worth investigating.  An as-of-yet unpublished study by Rosemary Waring at the University of Birmingham in the UK claimed that blood and urine levels of magnesium and sulfate rose significantly after 19 test subjects were immersed in a warm bath of water and Epsom salt for 12 minutes.

Presumably, the magnesium and sulfate ions were transported into the bodies of the subjects by crossing the skin.  Though we normally think of our skin as an impermeable barrier that separates “inside” from “outside,” a 2002 study conveniently confirms that both magnesium and sulfate ions (which are formed when magnesium sulfate, i.e. Epsom salt, is dissolved in water) can indeed be transported through the skin.  So, soaking an injured foot in an Epsom salt bath should lead to magnesium and sulfate being absorbed at the site of injury.

Although interesting, the relevance of this hinges on the usefulness of increasing magnesium or sulfate levels in the body.

To this end, there’s no reason to expect that a small increase in the concentration of these ions would have any effect on pain, inflammation, or injured tissues.  Waring’s study also has some significant drawbacks, not the least of which is that it hasn’t even been published or peer-reviewed.

Further, the temperature of the warm water baths reported in the study are a scalding-hot 120-130 degrees Fahrenheit! Irregularities of this magnitude should make us at least suspicious of the findings of the study.

Osmosis

Moving on, there is another theory about why Epsom salt baths might help with injuries.  Through a process called osmosis, soaking in a properly-prepared solution could alter the concentration of water in the tissues around an injured area.

When two solutions (say, an Epsom salt bath and your body’s inner workings) are separated by a membrane like your skin, water will diffuse across the membrane in the direction of the higher concentration solution.  So, an Epsom salt bath could hypothetically exert some osmotic pressure on the water inside your body, drawing it through your skin.  Though water can indeed permeate at least slightly through your skin, this osmosis theory has some flaws as well.

• First, swelling is not usually the problem when it comes to overuse injuries in runners.  An acute injury, like a sprained ankle, involves a lot of swelling, but chronic tendonitis or other common running injuries involve no inflammation or fluid buildup.  While animal research has indicated that highly concentrated salt solutions can draw out fluid and reduce swelling in acutely injured areas, rabbits with broken legs are a long ways off from runners with an overuse injury.

• Further, the concentration of Epsom salt you’d need in your solution is quite high to actually get osmotic pressure in the right direction—over half a pound of Epsom salt per gallon of water, based on some back-of-the-envelope chemistry calculations.  This is far more than the concentration used by Rosemary Waring in her study (0.08 pounds per gallon), and worse, there’s nothing special about Epsom salts in this respect—regular table salt would work fine too when it comes to osmosis.

Conclusion

Barring future research, it’s very hard to justify an Epsom salt bath over a traditional ice bath or hot water bath for treating an injury.  Though Epsom salt is dirt-cheap, no research supports any direct effect on injury recovery, and none of the theories forwarded about how Epsom salt might help in indirect ways hold up to any scrutiny either.

For treating your running injuries, you are better off following the guides here on Runners Connect about better-tested running injury treatment protocols like rest, cold water immersion, contrast baths, and rehab exercises.