Epsom Salt Baths for Post Run Soreness: Does It Really Work?

Last Updated on August 3, 2018 by Heather Hart, ACSM EP-C

For as much time as I spend defending this sport against all of the “running is bad for your knees” naysayers, I will be the first to admit that running can, and often does, hurt.   Running long distances, especially when you are new to them, can leave you hobbling around for a few hours post run, desperately seeking some sort of relief from the discomfort.

The plethora of information about how to properly recover can be just as overwhelming as the information about how to properly train.   Every dedicated runner has their preferred recovery trick, whether there is any proven benefit to that trick or not. Compression socks. Foam rolling. Ice baths. And the one I want to talk about today: Epsom Salt baths.

Poll a group of endurance athletes on what they do for post long run soreness, and I guarantee that multiple people will answer “Epsom salt bath!” The claim is that by soaking in a bath with Epsom salts, otherwise known as magnesium sulfate, will help prevent and heal muscle soreness, joint pain, and detoxify the body.

Let’s dig deeper into how this might, in theory, work.

Magnesium and running:

Magnesium is a critically important mineral found in the human body, and is heavily involved in protein synthesis, energy production and detoxification. Studies show that most humans are deficient in magnesium.  In fact, less than half (48%) of the US population consumed less than the required amount of magnesium from food (source).  Runners in particular are at a risk for magnesium deficiency,  as research has shown that exercise not only induces a redistribution of magnesium in the body to accommodate metabolic needs, but exercise also increases urinary and sweat losses that may increase magnesium requirements by 10-20% (source).

Running: magnesium depleter.

Therefore, the claims are that by soaking in a tub full of Epsom salt, magnesium and sulfate are absorbed through your skin, make up for those deficiencies, and magically aide the protein synthesis and detoxification of your body, resulting in less soreness.

Makes sense, right?  Well it could…except that the human body doesn’t exactly work that way.

Our skin is relatively waterproof, a design that by nature helps us keep all of the “good” stuff inside our bodies, and the “bad” stuff out . If our skin wasn’t essentially non-permeable, we’d be constantly struggling to keep out toxins and keep in everything else we need in order to survive. Therefore, the idea that a quick soak in a tub can both cause minerals we are supposedly deficient in to soak into our body, all while the bad “toxins” soak out, seems a little far fetched.

Old Wives Tale?

In fact, a quick Google search, or even an extensive pubmed.gov search for that matter, will turn up empty with reputable, peer reviewed research that says magnesium and sulfate are absorbed across the skin, or that Epsom salt baths actually work as a means of post workout recovery. In other words, science does NOT currently back the claims of Epsom salts when it comes to sore joints and muscles, nor the claims that transdermal magnesium absorption (i.e. sitting in a bathtub full of magnesium sulfate) is a successful way to increase magnesium levels in the body.

So is an Epsom salt bath soak a complete waste of time?

Not exactly.

There is no denying that a nice, hot bath can help relax you, both mentally and physically. This of course, is the complete opposite concept of the post long run ice bath, which I would argue is not relaxing AT ALL (I can’t bring myself to do them anymore)…even though it still may help ease post run soreness.

Freezing cold soak in Twin Lakes, Leadville, CO after stage 2 of the TransRockies Run. Did I mention it was cold?

But let’s get back to the hot bath.

Adding essential oils or aromatherapy Epsom salts to your bath an help you mentally unwind from the stressors of training, and life in general. Relaxing your mind may help you relax your muscles, which can help soothe stress, aches, and pains associated with hard training. And some research even shows that warm muscles are likely to be less tense than cold muscles.

Plus, there is always the argument of the placebo effect. If you feel better after soaking in a hot tub full of Epsom salt, then do it.  There is likely little to no risk in a relaxing bath full of Epsom salts.

But…that magnesium deficiency? Don’t leave me hanging! 

Right.  The recommended daily allowance for the general population is a minimum of 300-350 mg of magnesium for women, and 400-450 mg for men.  But research suggests that runners and endurance athletes can safely consume 500-800 mg of magnesium a day, and there is debate as to whether even that amount is enough.  So where do you get it from?

So much magnesium! 58 mg per avocado, to be exact.

We’ve established that you cannot simply cure your magnesium deficiency through osmosis in a relaxing bath. The best way to up your magnesium levels?  Food and supplements.

Magnesium is found naturally in a number of healthy foods, such as spinach, pumpkin seeds, brown rice, avocados, dark chocolate, and so much more.  Check out the post “The 10 Best Foods Highest in Magnesium” to learn more.

Another option, that should be used in addition to, and not in place of, food based magnesium sources is a magnesium supplement.   An example of a sports specific magnesium supplement includes ZMA Sports Recovery from NOW Sports (disclaimer: that’s an amazon affiliate link), which is a supplement that combines Zinc, Magnesium, & Vitamin B-6. There are a number of other magnesium supplements available on the market.  If you choose to take a supplement, ALWAYS consult your physician first to ensure that the supplement is right for you, and to discuss proper dosing for your needs.

NOW Foods Zinc, Magnesium, and Vitamin B-6 Recovery Supplement

Back to the Epsom salt baths:

So in conclusion, yes many of us are deficient in magnesium, and runners might be extra susceptible to this deficiency.  At this time, science has yet to provide concrete evidence proving that we can fix this deficiency, nor alleviate sore muscles, from simply soaking in Epsom salts in a bathtub.  I’m sorry to break it to all of you devout fans, but it appears use of Epsom salts for healing sore muscles is likely an old wives tale, and you are experiencing a placebo effect.   But  all of that said: will an Epsom salt bath hurt you?  Chances are no, not at all.  If anything, it will help you relax…and your long run legs deserve the break!  So soak in that tub, my friends!  You’ve earned it!