SaveYourself.ca •Sensible advice for aches, pains & injuries
 
For blind and low-vision visitors, an audio version of this article is freely available on request to visually impaired visitors. Please email requests for audio to paul@SaveYourself.ca and I will send a download link within a day. There are audio versions of seven other popular articles on the site.  This image is linked to a page with more information, or see SaveYourself.ca slash   audio.

Do Epsom Salts Work?

There is no good reason to believe that Epsom salt baths aid recovery from muscle pain, soreness or injury

8,000 words, published 2006, updated 2013
by Paul Ingraham, Vancouver, Canadabio
I am a science writer, the Assistant Editor of ScienceBasedMedicine.org, and a former Registered Massage Therapist with a decade of experience treating tough pain cases. I’ve written hundreds of articles and several books, and I’m known for sassy, skeptical, referenced analysis and a huge bibliography. I am a runner and ultimate player, and live in beautiful downtown Vancouver, Canada. • full bioabout SaveYourself.ca

illustrations by Paul Ingraham, Gary Lyons

An audio version of this article is freely available to visually impaired visitors. Please email requests for audio to paul@SaveYourself.ca and I will send a download link within a day, but usually much faster. There are audio versions of seven other popular articles on the site.An audio version of this article is freely available to visually impaired visitors. Please email requests for audio to paul@SaveYourself.ca and I will send a download link within a day, but usually much faster. There are audio versions of seven other popular articles on the site. audio version available infoThis is one of seven articles available in audio format as a free bonus for e-boxed set customers. For more information, see SaveYourself.ca Audio Articles.

SHOW SUMMARY Epsom salt in your bath is cheap and harmless and it makes bath water feel “silkier,” so there’s no reason to ban it from your life. However, it probably doesn’t do what you hope it’s doing. Although Epsom salt probably does have some physiological effects, it is unknown if there is a therapeutic effect on aches and pains … and somewhat unlikely. Most of the theories you hear are oversimplified and meaningless — for instance, nearly everyone says it is absorbed by osmosis, but that is false and impossible — and the known effects of Epsom salt don’t have much to do with common causes of pain. The heat of a nice bath is probably more therapeutic. The case for the healing powers of Epsom salt is mostly made by people selling the stuff, or recommending it as casually and imprecisely as an old wives’ tale.

Welcome to what is — oddly — one of the most popular articles on the internet about Epsom salts. It seems I have written more about bath salts than anyone else ever has. Many, many people who Google for Epsom salts end up right here. Incredibly, this means that I get some hate mail about Epsom salts. I’m not joking. Some people, apparently, feel very strongly about their baths.

Epsom salts are magnesium sulphate heptahydrate, usually shortened just to magnesium sulphate (note also the American spelling “sulfate”). It was originally obtained by boiling down mineral waters at Epsom, England. It is quaintly referred to in the plural — Epsom salts instead of Epsom salt — but it’s just one kind of salt, and other than tradition there’s no more reason to say “salts” than there is to say “please pass the table salts.”

Other than tradition there’s no more reason to say Epsom “salts” — plural — than there is to say “please pass the table salts.”

Other than tradition there’s no more reason to say Epsom “salts” — plural — than there is to say “please pass the table salts.”

Supposedly good for pain in your muscles

A cup or two of Epsom salt in a bath supposedly relieves pain — specifically, muscle pain from over-exertion (delayed-onset muscle soreness), conditions like myofascial pain syndrome (trigger points, or muscle knots) and fibromyalgia — and speeds healing from minor injuries such as sprains and tendonitis. But notice that there are two quite different ideas there: “relieves pain” and “speeds healing” are as different from each other as a flying dream (good and not that rare) is from actually flying (better and rather miraculous) — so which one we’re talking about makes a difference.

Claims and recommendations of this nature are widely published, and can be found by the thousands with a quick Google search. Bags and cartons of Epsom salts are available at any drugstore, with instructions for use in baths. I have a package right here.1 It says:

Dissolve desired amount (1–2 cups) of crystals in a hot bath to produce a mineral water treatment to aid in the relief of muscular aches and pains.

When I went to school, my instructors suggested Epsom salt baths as a good thing to prescribe to our clients. No scientific basis for this idea was ever presented: it was just one of those things that everybody “knew,” a folk remedy justified by the generations of wise old wives and bathers. The physiology of it certainly wasn’t made clear to us. No evidence for the efficacy of Epsom salts was ever presented, nor did it seem necessary to talk about it.Occasionally someone made a vague reference to “detoxifying” the muscles, perhaps “by osmosis.” Nothing more exact was ever discussed because, frankly, I am sure that not one person in the building could have even named the molecule “magnesium sulphate.”2

Ever since then, I have wondered if there was anything to it. I am strongly skeptical of all health-related claims involving “toxins,” mostly because people who toss that word around almost never actually know which specific toxins they are talking about.3 I have thoroughly studied the subject of post-exercise muscle soreness — which is probably the leading cause of hot baths — only to discover that it’s basically been proven that there are no known remedies for it.4 And after a long, hot Epsom salt bath of my own one night — which had no apparent effect on my unusually sore muscles — I decided it was time for a reality check.

Does an Epsom salt bath do anything?

The chemical structure of Epsom salts … so that you know this is a <em>serious</em> article.

The chemical structure of Epsom salts … so that you know this is a serious article.

The chemical structure of Epsom salts … so that you know this is a <em>serious</em> article.

The chemical structure of Epsom salts … so that you know this is a serious article.

A word from my sponsor … which is, um, me …

This educational website offers more than free articles about pain problems, but it is also partially funded by the sale of 8 e-books for people with pain problems. If you are researching Epsom salts because you have frustrating muscle pain, you may also want to read the free introduction to my book about muscle pain — by far the most advanced self-help guide on this topic published anywhere.

Save Yourself from Trigger Points & Myofascial Pain Syndrome

Myofascial trigger points — muscle knots — are increasingly recognized by all health professionals as the cause of most of the world’s aches and pains. This detailed tutorial focuses on advanced troubleshooting for patients who have failed to get relief from basic tactics, but it’s also ideal for starting beginners on the right foot, and for pros who need to stay current. 193 sections grounded in the famous texts of Drs. Travell & Simons, as well as more recent science, this constantly updated tutorial is also offered as a free bonus (2-for-1) with the low back, neck, muscle strain, or iliotibial pain tutorials. Add it to your shopping cart now ($19.95) or read the first few sections for free!

A crystal of magnesium sulphate heptahydrate — Epsom salt.

A crystal of magnesium sulphate heptahydrate — Epsom salt.

Almost no Epsom salt science

My search for scientific evidence concerning Epsom salt baths was disappointing. I was unable to find even a single scientific paper studying their effect on body pain. Folk remedies are often generally neglected by researchers, but not usually so completely. There are usually at least a few experiments testing popular remedies kicking around. Why wouldn’t the use of Epsom salts for muscle soreness be similarly blessed?

There is plenty of research relevant to other medical uses of Epsom salts.5 For instance, on my package of Epsom salts, instructions are also given for internal usage as a laxative — which does work67 and is actually FDA approved and probably the most common and generally known medical usage. Other uses of magnesium sulphate include the treatment of irregular heart rhythm, low blood magnesium,8 eclampsia,9 and severe tetanus.10

But there appears to be simply nothing at all published about alleviating aches and pains or “detoxification.” Apparently, researchers just aren’t interested, or (more likely) they simply can’t get funding for the work.

It seems like researchers just aren’t interested in studying the effect of Epsom salts on muscle pain.

Strangely, Epsom salt baths do not even rate a mention in Home Remedies: Hydrotherapy, massage, charcoal, and other simple treatments, a large and credibly referenced compendium of traditional remedies assembled by a pair of doctors. They describe five medicated baths — alkaline (soda) baths, starch baths, oatmeal baths, peroxide baths, and sulfur baths — for conditions ranging from poison ivy rashes to diabetic gangrene (!), but they never mention Epsom salt baths. Could they possibly have just neglected it? Or is it more likely that Epsom salt baths simply have no (clear, known) medical usage?

In the perfect absence of any testing, all we can do is speculate about the possible mechanisms of action. Does brining yourself like a turkey do any good? Can you pickle your pain away? Is there any plausible way that Epsom salts could have an effect on your sore muscle tissue, or on the healing of injuries?

“(With) a grain of salt,” (or “a pinch of salt”) in modern English, is an idiom which means to view something with skepticism, or to not take it literally.

“Detoxification” and “osmosis” explain nothing about Epsom salts

Regardless of whether Epsom salts baths work, it’s important to understand that the words “detoxification” and “osmosis” are virtually the only explanations offered — and they are both hopelessly misleading. Usage of these terms mostly just reveals a poor understanding of both toxins and osmosis. If we are to understand Epsom salt, we need to get past this and understand it for the right reasons.

The osmosis/detoxification explanation is never actually clarified in any detail by the people tossing the words around. Presumably it is intended to mean — roughly — that either osmosis is actually a mechanism of detoxification (getting something nasty out of the body through the skin), or that osmosis is the mechanism by which something in Epsom salts can get into the body and then have a detoxifying effect.

People often mistakenly believe that osmosis refers to the movement of substances — ions and molecules — across a membrane. Alas, that is simply wrong by definition. Osmosis does not move particles. Osmosis refers to the movement of water only across thin membranes, towards higher concentrations of dissolved substances.11 Take it from the Osmosis Cats!show cats12

You can demonstrate this clearly by soaking a potato in salty water: the water is “sucked” osmotically out of the cells, they lose their plumpness, and the potato goes limp. Poor little potato. It’s the water that moves around. (Or cats.)

Can salt disinfect? Osmosis and all the wee beasties

Reader Dorrie B. pointed out something interesting: Epsom salts might be an effective treatment for topical skin infections, as salt is certainly inhospitable to microganisms. Osmosis may not be able (by definition) to transport salt ions across the skin, but it certainly isn’t kind to bacteria in this equation: it sucks them dry.

An Epsom salt bath definitely cannot disinfect a puncture wound, as one of my readers was told. A strong salt solution is anti-bacterial, but the problem with rusty nails is the risk of deep injection of Clostridium tetani — beyond the reach of any soak.13

But this is also a great example of how complex these questions can be, because salt bathing might also damage populations of other bacteria on the skin, resulting in higher vulnerability to infection.14 Do people who bathe or swim in salt water regularly suffer any ill effects? Are they more susceptible to new infections? They might well be: even a 10% or 20% difference would not be obvious to the victims, but would nevertheless be clinically significant and biologically interesting.

Likely that research hasn’t been done, but my point is just that it’s really surprisingly difficult to say whether or not a given biological effect is “good” — it’s almost never that simple, and it’s a good thing to bear in mind throughout this article.

Skin is waterproof (and maybe Epsom salt proof)

So, however Epsom salts get into the body, if they do, it’s not by osmosis. Osmosis doesn’t work through the skin. Skin is almost completely waterproof. If it weren’t, you would dehydrate like an earthworm on a sunny sidewalk. (You do dehydrate significantly by sweating in a bath, of course.15 But Epsom salts do not increase that.16)

The top layer of the skin, the stratum corneum, consists of dead cells stuffed with a kind of embalming substance, keratin, a fibrous protein. The cells are mostly impermeable to water, and additionally we have glands that coat the skin in waterproofing oils. When those oils wash off, the dead skin cells can soak up water and swell, like soaked beans. Since the top layer of the skin is attached to the layers below, which do not swell, the top layer wrinkles or “prunes.”17

That swelling of the superficial skin cells is not due to osmosis, but rather to a limited “capillary action” in which water molecules flow into small spaces. (Paper towels absorb liquid the same way.) The stratum corneum is mostly waterproof precisely because osmosis is not a significant factor here. Those cells are dead. They contain mostly just dry keratin — not fluid containing dissolved substances which could osmotically “suck” water into them.

Furthermore, the stratum corneum is generally an effective barrier to diffusion: ions and molecules dissolved in water cannot generally pass through the stratum corneum, again because there is virtually no water in the outer layers of skin for them to diffuse through. This is not to say that nothing gets past the skin, just not much.

Booze, for instance. You can’t get drunk through your skin, alas. Contrary to the Danish myth. As proven by Danish researchers in late 2010.18 It’s funny, but it’s not a joke.

The point is that it’s not exactly obvious to people what substances can get through the skin. Ask your friends: most of them will guess that some alcohol probably does get through the skin — maybe not enough to get drunk (or booze baths would be a more popular practice), but some. In fact, none gets across.

Skin is lipid (fat) permeable, which is why many solvents are quite dangerous to us, and why we can get rashes from toxic plant oils, and why we can easily get a medicine through it (as in nicotine or hormone patches). But a great deal else is kept out — and a good thing, too! The skin is a vital defensive layer, a physical barrier that prevents infection and dehydration.

When I wrote the first version of this article in 2005 or so, there was no evidence that Epsom salts could even get past the skin, nor any likely mechanism for it, and it seemed quite implausible. I predicted that salt, like booze, would fail to get through the skin if you tested it.

Yes and no. There is now evidence both ways.

Evidence against absorption: Israeli soldiers smear magnesium all over themselves in high concentrations and it still doesn’t get inside

This quote from a book by a doctor19 was submitted to me by a reader as an “authoritative” opinion on absorption:

Regularly bathing in hot water to which Epsom salts have been added can help draw out toxins from the skin.

This is not an authoritative opinion: it’s a vague and unsupported one. That anyone would mistake it for authoritative is rather depressing.20 The only thing that can determine whether magnesium heptahydrate is absorbed from a bath is careful, thorough testing — opinion is irrelevant, even from a real expert.

Fortunately, not all my mail is depressing. Hat tip to reader Bryan B. who found an interesting study and sent it to me. (I love it when readers do that.) It’s a safety study of a lotion developed “to improve protection against chemical warfare agents.”21 Like suntan lotion, but for chemical burns. Yikes.

This lotion had rather a lot of magnesium in it. And soldiers were not poisoned by the magnesium. Indeed, it didn’t appear to cross the skin at all: “there were no significant differences in magnesium levels between the placebo and the study groups in any of the applications.” The delivery system — lotion — could be quite different than soaking in water with dissolved magnesium sulfate. But I agree it’s pretty good evidence that absorption is minimal or nil.

And that contradicts virtually the only other science on this topic.

Awkward.

Evidence for absorption: Rosemary Waring’s results show that magnesium sulphate does get past the skin

In 2006, Rosemary Waring, a British biochemist at the University of Birmingham, did a nice science experiment with Epsom salts.22 She did more or less exactly what any curious person would do if she wanted to know whether or not Epsom salts can get past skin: she measured magnesium and sulphate in the blood and urine both before and after people bathed in Epsom salts.

Dr. Rosemary<br>Waring

Dr. Rosemary
Waring

She found them to be higher after the baths! 16 out of 19 people had more magnesium and sulphate in their blood after the baths than they did before the baths.23 Fascinating!

Dr. Waring’s results are straightforward. No therapeutic effects of Epsom salt were studied or claimed — she just studied absorption, and did not try to make any more of it, showing the restraint of a pro. What could be simpler?

I was so interested in these results (although still a bit skeptical) that I contacted Dr. Waring by email. “I agree that it is a bit surprising,” she replied, “but the results are certainly there and in fact there are hints in the past literature that this could happen.”

Better still, Dr. Waring told me that a colleague of hers in London has done another experiment which showed that “magnesium sulphate can cross human skin using pieces of excised human skin in a special apparatus.”

Now eight years later, neither experiment has yet actually been published,24 and that’s a reason for caution. It is a basic rule of science that evidence can’t really be taken too seriously until it has been exposed to peer review and repeated by other scientists. Just because experimental results haven’t been replicated yet doesn’t mean we ignore them, but it does mean that we have to take them with a grain of salt. (That pun was simply unavoidable — so sorry.)

Meanwhile, what can we make of Dr. Waring’s results? One thing only so far …

  1. There could be a mechanism for getting magnesium and sulphate across the skin!

It’s not much, but it’s important. And when I found the new evidence, I embraced its implications. (That’s how science works. That’s why being anti-science is like being anti-honesty.25 I happily admit that Dr. Waring’s results might mean that I was simply dead wrong about the absorption question originally.)

How would it work, this crossing of the skin, if it’s happening? Dr. Waring: “I don’t have any evidence as to how magnesium sulphate crosses the skin, though I have always assumed that it simply diffuses across the stratum corneum, helped by the fact that it’s in a hot bath.” Molecules certainly do diffuse much more quickly in heat. I’m still not clear myself on how ions diffuse through the fairly arid and water-proof stratum corneum, but it does seem that they are getting through it somehow. There may also be an active transport mechanism — that is, skin cells may actually spend energy to drag salt molecules into the body.

(But it still ain’t osmosis, and that’s still well worth emphasizing.)

Maybe up your bum? Um …

When you encounter surprising results in science, don’t just settle on the first explanation that comes to mind — it could easily be wrong. Dr. Waring says that she “assumed that it simply diffuses across the stratum corneum,” and that certainly is possible. But what other explanation could there be for the results? How else could magnesium sulphate have gotten into the bloodstream in her experiment? Reader Adrian J. had an unusual idea:

Is it possible that the salt diffuses across the epithelium in the anus if the rectum relaxes to some degree in the warm water?

Wow, that’s some awesome lateral thinking! And I think it’s plausible. But I find myself (uncomfortably) wondering ... just how much do I relax in a hot bath? That much? And how much salt could diffuse across that more permeable but much smaller membrane? It’s a small target! And I shudder to think of the measures required to test this hypothesis! For what it’s worth, we know that alcohol absorbs quite handily through the rectum — rather too well, in fact, so do not try at home.26 But it has to be pretty much injected. (Live a little: click that footnote!)

A number of readers have asked if the vagina might be an absorption route. A fair question, but this has the same problem as anal absorption: too small and too tight. After quizzing several amused female friends about it, I am confident that it would be highly irregular for any respectable quantity of bath water to percolate into one’s ya-ya.

And you thought an article about salt baths would be boring! No wonder this the most popular Epsom salts analysis on the internet!

Another remote possibility for absorption: salts could be inhaled though bath vapors. Lying in hot salt water, with your nose and mouth only inches from the water, it’s slightly plausible — if salt can be carried by vapours (probably), and if enough of it came into contact with mucus membranes to be absorbed in meaningful quantities (hmm), it might explain Waring’s result. A hat tip to reader James L for that suggestion.

What could magnesium and sulphate ions do once they cross the skin?

If Epsom salts do get across the skin … so what? Is it any good to have a few extra ions of magnesium and sulphate kicking around your bloodstream? The rest of this article continues to mostly cast doubt on the possible therapeutic effects.

There might well be a therapeutic effect, but we have no information about what it is, how it works, what it works for, how strong the effects are, what side effects there might be, and so on. The increased levels of these ions shown by Dr. Waring’s experiment are small, about a 10% increase on average (and none in some subjects, remember). The concentrations could also be quite different in the fluids between cells — she didn’t measure that. It is still completely unclear what effects these ions could have on your tissues when they arrive.

There is no doubt that magnesium sulphate has effects on physiology. Several of those effects are reasonably well known, including a few common medical applications mentioned earlier. There are also unpleasant effects. But, judging from the established medical uses of Epsom salt, there is definitely no particular reason so far to believe that having more magnesium or sulphate in your blood is going to be much use to you — unless you have eclampsia or tetanus or autism.27

The closest thing there is to a relevant science experiment is one study of injected magnesium sulphate which found that it “did not reduce muscle pain” and caused “unpleasant side effects.”28 Yuck! Not exactly encouraging!

So there’s not really any particular reason to believe anything about the therapeutic effects of Epsom salts for aches and pain. We can really only speculate. And speculating about basic biology is really difficult. It’s a great way to be wrong.

No matter what it can do, it can’t do everything

This is a classic problem with all kinds of supposedly amazing pain cures: pain has too many different causes for one medicine to be really effective.

There are many types of muscle and joint pain that have little or nothing at all in common with each other physiologically. For instance, the pain of fibromyalgia originates in dysfunction of the central nervous system, which is completely different from the pain caused by exercise, which in turn is completely different than the physiology of trigger points. Even “basic” muscle pain is incredibly complex and has many flavours.29

While it’s certainly conceivable that increasing levels of magnesium and/or sulphate ions in the bloodstream could help with some pain problems, it’s extremely unlikely that it would help enough different kinds of pain to be generally “good for” pain” This is a really important logical point! Nothing can be a magic bullet that will help all types of pain, or even more than a couple of them.

Similarly, Epsom salts probably cannot simultaneously perform the two tricks most often touted: “relieve pain” and “speed healing.” Those are completely different things.

They might even be mutually exclusive. For instance, the primary source of injury pain is inflammation — a complex and painful physiological process intended to … wait for it … speed healing. Indeed, the only known mechanism by which you could recover faster from an injury would be to increase inflammation. If bathing in Epsom salts did that, it would make you hurt more, not less. Of course, there could be other ways to speed up healing — in an “anything’s possible” kind of way — but it’s still pretty far-fetched that a single molecule could pull off both that miracle and reduce pain at the same time.

The point here is just that the conventional wisdom is pretty murky.

ZOOM

Salt has been used for well, just about everything. Like these effervescent brain salts. Cory Doctorow: “The best thing about effervescent brain salt is that it’s not immediately clear whether it’s salt to make effervescent brains even more delicious, or salt to give you an effervescent brain, or effervescent salt for brains. Also, it appears to come in a Tabasco bottle, and everything that comes in a tabasco bottle is always awesome.

ZOOM

Salt has been used for well, just about everything. Like these effervescent brain salts. Cory Doctorow: “The best thing about effervescent brain salt is that it’s not immediately clear whether it’s salt to make effervescent brains even more delicious, or salt to give you an effervescent brain, or effervescent salt for brains. Also, it appears to come in a Tabasco bottle, and everything that comes in a tabasco bottle is always awesome.

What’s a calcium channel, how do Epsom salts block it, and who cares?

Generally speaking, explanations for the benefits of Epsom salts are really vague, as discussed above: “osmosis and detoxification.” Once in a blue moon, you’ll see Epsom salts (or magnesium in particular) more exactingly described as a “calcium channel blocker” with the implication that this is obviously “good for pain.”

Unsurprisingly, this is another misleading oversimplification. Although it’s more specific and impressive sounding, it’s not a heck of a lot more meaningful than “detoxification.”

Calcium channels are itsy bitsy — molecular scale30 — holes in cell walls that let calcium in and out as a trigger for a bunch of biochemical business. They exist primarily in muscle tissue (including the heart), blood vessels, and neurons. There are a number of druggy ways to interfere with them, including magnesium. Calcium channel blockage is a reasonably well understood bit of physiology, and the main clinical usage of calcium channel blockers is to decrease blood pressure by reducing the strength of muscle contraction in the heart and blood vessels. Although other effects undoubtedly exist, there is no particular reason to believe that they have any potent effect on any flavour of pain.

Lots of people are walking around with calcium blockers in their blood. Calcium blockers aren’t rare drugs. Since there are numerous drugs that block calcium channels in various ways, it’s a bit implausible that there would be some kind of powerful pain-killing effect that no one’s noticed. I don’t think, as a rule, that people on calcium channel blockers are walking around feeling no pain, like a superpower.

Yes, it is possible that magnesium absorbed through the skin does something different, something good, for certain kinds of pain. After all, different calcium blocker drugs have different effects! But there’s not a shred of good, direct evidence of it. So it really boggles the mind that anyone would toss this idea around with any confidence. Seriously, they’re pretty much making it up as they go — wild speculation.

I don’t think that people on calcium channel blockers are walking around feeling no pain.

Magnesium as a pain-killer after surgery

There is some limited evidence that magnesium (just that ion) may reduce pain, perhaps because it is a “calcium channel blocker and N-methyl-D-aspartate antagonist,” as in a 2009 experiment.31 However, this is uncertain science. Several studies have been done, with conflicting results. Most were reviewed in 2007:32 four showed a positive effect, seven showed no effect greater than a placebo, and in one experiment the subjects actually experienced more pain (ouch).

And so, although “the biological basis for its [magnesium’s] potential antinociceptive effect is promising,” the authors concluded that no pain-killing effect could be found. So much for the miracle of calcium channel blockage: it fails the “impress me” test. It seems unlikely that magnesium would fail to relieve pain in those tests, and yet somehow succeed when absorbed from Epsom salts baths.

Clearly, this mystery is not solved yet. While there is a plausible mechanism for magnesium ions reducing pain, it is clearly neither well understood nor reliable. Do you suppose the picture is any clearer for Epsom salts in your bath? Don’t bet on it!

Sulphate supplementation

I asked Dr. Waring to speculate about the therapeutic effects. She pointed out that patients with rheumatoid arthritis are known to have low sulphate levels. Molecules produced by the inflamed tissues in these patients may interfere with the production of a protein that is used to produce sulphate from another molecule (cysteine), thus lowering sulphate levels.33

However, low sulphate levels are a possible result of having rheumatoid arthritis, not a cause — and thus boosting them back up again will not necessarily solve anything. And even if it did, that’s a therapeutic effect that is very particular to rheumatoid arthritis — a serious, agonizing joint disease — which probably has little or nothing to do with the kinds of pain that most people put Epsom salt in their baths for.

It would be great if Epsom salt baths helped people with rheumatoid arthritis, but good evidence of that would, in a way, pretty much shoot down the other claims of therapeutic effect, which rely on completely different ideas about how and why Epsom salt might work. But, of course, there is as yet no evidence one way or the other.

Mixing up the effects of salty and non-salty baths

Obviously non-salty baths have some benefits of their own. Epsom salts routinely get the credit for these benefits. It goes like this:

  1. Patient has a problem and tries non-salty hot baths or soaking. However, because it’s just a bath and expectations are low, this effort is never particular diligent. This is key to the setup: the patient has never really given non-salty soaking a good try.
  2. Patient gets the idea to try Epsom salts! This seems much more promising.
  3. Thus inspired, the patient proceeds to soak quite diligently — much more diligently than ever before.
  4. When some benefit is then observed, patient attributes this to the salt — of course. Maybe it is, but maybe it’s just the unusual regularity of the nice soaking. The point is that we obviously can’t know … but the patient is now officially biased.
  5. If the benefits are at all notable, this person will usually start proclaiming to anyone who will listen that they "know" that Epsom salts work.
  6. When challenged (“It might be just the hot bath, eh?”), they will almost certainly object and claim (correctly!) that they have tried simple hot soaking without results. They have indeed. But it was never actually tried well enough to really know.

Tricksy, the human mind is.

Consider the source!

ZOOM

Dr. Waring’s results are irrelevant to the popular idea of “osmosis,” which refers to the movement of water, not molecules. Nor do her results imply anything about that other popular concept associated with Epsom salts, “detoxification.” And yet, 99% of the time, “osmosis” and “detoxification” are the concepts presented as the justification for bathing in Epsom salts. Can you trust advice that simplistic?

The detoxification claim implies either that Epsom salts somehow “suck” toxic substances out of your muscle tissues, or that Epsom salts get into your system and then somehow “clean up” some toxic substances that they encounter. There is no scientific evidence at all for either of those basic detoxification scenarios, and both involve some seriously optimistic assumptions, leaps of logic, avoidance of detail … all made by people who are usually trying to sell the stuff.

Epsom salt bath prescriptions are invariably brief, and are often accompanied by really strange claims of healing powers. For instance, I found one website that recommended taking Epsom salts internally as well as bathing in them:

Researchers in nutrition, through controlled experimentation, have found that Magnesium sulphate accelerates the body’s healing time by 30%. As an example, if an injury required three weeks to heal under normal or standard conditions, it would only require two weeks to heal if Magnesium sulphate was added to the diet as a nutrition [sic].34

That’s really ludicrous. Accelerated healing time is a comic book concept — something Wolverine does — not an even remotely legitimate medical concept. And imagine the unpleasant surprise of the hapless reader who takes this advice when they discover the laxative effects of ingesting Epsom salts! Naturally, no source for this alleged experiment was given.

Epsom salts bathing is often recommended carelessly and overconfidently, without any genuine knowledge of the physiology or science (or lack thereof). Those who claim to “know” that Epsom salts work cannot seem to demonstrate that they also “know” much about physiology or science. While it certainly remains possible that there is a therapeutic effect, it’s pretty clear that we shouldn’t take their word for it.

Nice-feeling water and floatation therapy

Is there any other reason to put Epsom salts in your bath? Well, Epsom salts dissolved in your bath does make the water feel nice. No research is required to prove that: just try it! Most people agree that the water feels smoother, slicker, silkier.

And it makes you floatier! But only ever so slightly. High concentrations of Epsom salt in your bath will increase the water’s specific gravity (density) to the point where you will start to float — just like in the Dead Sea, or Utah’s Great Salt Lake — because the body is, on average, much less dense than salty water. The concentrations of salt required for floatation therapy are much higher than Epsom salt packaging recommends, by the way.35 However, any salt in your bath — Epsom or otherwise — is going to make you at least a little bit lighter in the water.

Most people agree that Epsom salts make water feel “smoother.”

The purpose of floatation therapy is primarily to reap the benefits of deep relaxation, which are noteworthy.36 It sounds lovely to me — but irrelevant to the relief of muscle aches and pains except via the straightforward (and perfectly legit) mechanism of relaxation.

Something like a conclusion about Epsom salts

I can do no better in defense of Epsom salt bathing for aches and pains than “anything is possible.” There is no good or specific reason to believe that bathing in dissolved Epsom salts will have the slightest effect on muscle soreness or injury recovery time. Although this folk wisdom may someday prove to have a sound rationale, clearly there is none that its advocates have thought of — or even tried to think of, it seems.

There’s even decent evidence that Epsom salts can’t even get past the skin barrier — Israeli soldiers can smear on magnesium rich cream without the slightest effect on their blood levels of magnesium. That’s pretty damning.

On the other side of the evidence, thanks to Dr. Waring, we know that it’s still possible that we are a living experiment in absorbing magnesium sulphate ions every time we bathe in dissolved Epsom salts! And maybe, just maybe, they do something worthwhile once they get past the skin. And it’s very cheap, and almost certainly safe — just as no one is obviously getting any miracle cures out of Epsom salt bathing, they aren’t suffering any obvious ill effects either.

So, why not? At the very least, they’ll make your bath feel silkier! And at most? Who knows — maybe those magnesium and sulphate ions do have some healing powers. It’s certainly not impossible. Just don’t buy into all the crap about osmosis and detoxification. As the old Scottish proverb says, “Always keep your mind open — but not so open that your brains fall out!”

About Paul Ingraham

I am a science writer, former massage therapist, and assistant editor of Science-Based Medicine. I have had my share of injuries and pain challenges as a runner and ultimate player. My wife and I live in downtown Vancouver, Canada. See my full bio and qualifications, or my blog, Writerly. You might run into me on Facebook and Google, but mostly Twitter.

Selected Reader Comments and Questions

This is a new section that I’ve just started in the fall of 2012. It will grow.

Industry protectionism for baths? A reader asks, “Why would the FDA allow studies to be published that show Epsom salts are more effective than their muscle relaxers and pain pills? For $1/lb of epsom salt this would kill their market and profits.” The FDA has literally nothing to do magnesium sulfate research. They cannot regulate it. Any Big Pharma/FDA conspiracy against Epsom salt is clearly failing, because the stuff is available literally everywhere, and the FDA actually approves it for use as a laxative and a variety of external uses. Approval seems like kind of a funny way of implementing an anti-salt agenda. In short, this question is just knee-jerk anti-mainstream medicine paranoia based on major misunderstandings of what the FDA is and how it works. Nevertheless, it is a concern I’ve often see expressed, so I decided it was time to address it here.

Ironically, if there is any relevant commercial bias, it is one in favour of Epsom salts. For instance, the Epsom Salt Council exists to promote the industry and is “eager to let everyone know the benefits of our product and … spread the word about the wonder that is Epsom salt.” They prominently publish uncritical and unequivocal claims of medical benefit on their website.

Ok so you don’t believe that Epsom salt will do anything in a bath. So how about sea salt? You believe it’s the same? Useless for muscle aches and stuff like that? Yes, I believe it is “the same,” at least insofar as it is “useless muscle aches and stuff like that.” Of course there is much more chemistry going on in sea water than Epsom salts, but not in any way that seems to make any practical difference. In fact, it’s pretty clear that people who swim in the ocean a lot are not enjoying impressive pain-killing benefits the rest of us are missing out on — which is yet another example of how the skin is a pretty effective barrier.

ZOOM
Electric baths

Do not try at home

Oddly, there are a lot of electric baths in medical history. Electricity was a wonderful way to make health ideas based on vitalism seem more real and science-y.

Maybe there’s a “bio-electric” function to epsom salts in water. There’s more and more being discovered about small electric/magnetic fields and how we are affected by them. Er, no, I think not. It’s not inconceivable, but it is pretty far-fetched. It’s generally true that biology ingeniously exploits most properties of nature to get things done, including electromagnetism, and we likely still have things to learn about that (that’s what the book The Body Electric was about, and despite its age and flaws it’s a darned interesting read). But whatever those systems might be, it’s super unlikely that they have any meaningful interaction with a slightly salty bath, let alone one that’s relevant to aches and pains. It’s even less likely that any such effect wouldn’t be much more obvious in, say, sea water. Even if salty baths just bestowed a vague feeling of well-being and vitality, like mountain air, that would be biologically remarkable … but still well short of a useful medical effect. And in fact salty baths do not have an obvious mountain-air like goodness.

Still need help with myofascial pain?

If you think this article is detailed, you should see my tutorial about muscle pain and myofascial pain syndrome! This kind of exhaustively researched writing about Epsom salts is only possible because I sell some of the other articles on this website. No writer can afford to create truly good, detailed content and then just give it all away: we have to make a living somehow. Please reward my efforts by taking a look at my tutorials. Although Epsom salts seem unlikely to be a significant source of relief, there are plenty of other options for self-treatment of muscle pain. SaveYourself.ca publishes an extremely thorough tutorial about myofascial trigger points (muscle knots):

Save Yourself from Trigger Points & Myofascial Pain Syndrome

Myofascial trigger points — muscle knots — are increasingly recognized by all health professionals as the cause of most of the world’s aches and pains. This detailed tutorial focuses on advanced troubleshooting for patients who have failed to get relief from basic tactics, but it’s also ideal for starting beginners on the right foot, and for pros who need to stay current. 193 sections grounded in the famous texts of Drs. Travell & Simons, as well as more recent science, this constantly updated tutorial is also offered as a free bonus (2-for-1) with the low back, neck, muscle strain, or iliotibial pain tutorials. Add it to your shopping cart now ($19.95) or read the first few sections for free!

Other interesting reading:

What’s New In this Article?

Wednesday, January 16, 2013 — Added an explanation of why it is probably a bad idea to use Epsom salts as a replacement for a tetanus shot after a dirty puncture wound.

Tuesday, August 7, 2012 — Added the first piece of evidence against the absorption of Epsom salt.

Tuesday, June 19, 2012 — Added a particularly awful example of a bad article about Epsom salts. See immediately above in the Further Reading section.

Friday, August 26, 2011 — Added picture of cats demonstration osmosis.

Some updates were missed.

Monday, June 28, 2010 — Added information about the effect of Epsom salt on bacteria on the kin.

Monday, March 22, 2010 — Corrected several typographic errors.

Previous updates unlogged.

Notes

  1. Of course! Can’t very well debunk it without trying it, can I? I’ve had many Epsom salts baths! BACK TO TEXT
  2. I still can’t remember it reliably, because chemical names stick in my head about as well as my cousins’ birthdays. Ambush me with the question sometime: “What’s the chemical name for Epsom salts? Schnell, schnell!” I’ll be stumped as likely as not. BACK TO TEXT
  3. The idea of “toxins” is usually used as a tactic to scare people into buying de-toxifying snake oil of one sort or another. It’s not that there’s no such thing as a toxin — obviously there are toxic substances in the environment. The problem is the kind of people who toss the idea around, the reasons they do it (profit), and the total lack of any specific claim or scientific knowledge or evidence to support it. It is so vague that it’s literally meaningless, except as a marketing message. Indeed, “detoxification” may be the single most common marketing buzzword in alternative health care, and yet exactly which toxins we’re talking about, or exactly how they are disposed of, is never explained by anyone selling a product that supposedly detoxifies — because they don’t know.

    The body deals with undesirable molecules in many ways. It eliminates some and recycles others; some are trapped in a safe place; and quite a few can’t be safely handled at all (metals). Most alleged “detox” treatments are focussed on stimulating an excretion pathway, like sweating in a sauna. But it’s not like sweating is broken and the sauna is fixing it! The only truly “detoxifying” treatments help the body eliminate or disarm molecules the body cannot process on its own. A stomach pump for someone with alcohol poisoning is literally “detoxifying.” So are chelation for heavy metals, and antivenoms.

    I cover the specific idea of “flushing” toxins in Should You Drink Water After Massage? (Massage is wonderful for all kinds of reasons — it doesn’t need the support of the idea that it detoxifies.) For more general consumer advocacy and education about toxins, see “Detoxification” Schemes and Scams (from QuackWatch.org).

    BACK TO TEXT
  4. For more detail, see another article on SaveYourself.ca, Delayed Onset Muscle Soreness (DOMS): The biological mysteries of “muscle fever,” nature’s little tax on exercise. Basically what it boils down to is that the top 5 effective treatments for muscle pain after exercise are:

    1. diddly
    2. zilch
    3. zip
    4. zero
    5. maaaaybe massage, but probably not
    BACK TO TEXT
  5. Swain et al. Magnesium for the next millennium. Southern Medical Journal. 1999. PubMed #10586828. See also the Wikipedia article magnesium sulfate (Wikipedia). BACK TO TEXT
  6. Izzo et al. The osmotic and intrinsic mechanisms of the pharmacological laxative action of oral high doses of magnesium sulphate. Importance of the release of digestive polypeptides and nitric oxide. Magnes Res. 1996. PubMed #8878010.

    “A common use for high doses of oral magnesium salts is to produce a laxative effect to treat constipation,” explain the authors of this scientific paper. “In the intestinal lumen the poorly absorbable magnesium ions (and other ions such as sulphate) exert an osmotic effect and cause water to be retained in the intestinal lumen.”

    BACK TO TEXT
  7. James et al. A comparison of cathartics in pediatric ingestions. Pediatrics. 1995. PubMed #7630676.

    This paper compared the effectiveness of different laxatives, showing that Epsom salts do indeed move the bowels along … but not as quickly as sorbitol.

    BACK TO TEXT
  8. As occurs with chronic diarrhea, magnesium malabsorption, alcoholism, diuretic use and a few other disorders. BACK TO TEXT
  9. Eclampsia is a dangerous and fairly common complication of pregnancy. BACK TO TEXT
  10. Muscle spasms caused by bacterial infection with Clostridium tetani, which produces the neurotoxin tetanospasmin. BACK TO TEXT
  11. I’m deliberately over-simplifying the definition of osmosis there, just for readability. Osmosis actually involves the movement of any solvent across a membrane. And water is a solvent, of course. I referred only to water in this context because, unless you bathe in turpentine, the only solvent in your bathing-osmosis equation is going to be good ol’ H2O. BACK TO TEXT
  12. A reader asked: “Isn’t that cat diffusion?” It would be if the cats represented solute (particles in a fluid). But here I have decreed that they represent solvent (water) … which makes it osmosis, and the cat is “flowing” across the membrane like water. Admittedly, the metaphor is a bit strained! But the definition is bang on. BACK TO TEXT
  13. There are a lot of microorganisms that might be on a rusty nail, but CT is the scary common one that can kill you very unpleasantly (a chance of death by muscle spasm, arg). The reason you get a tetanus shot in that situation is that it is a very effective just-in-case prevention, good bang for buck. The idea that anyone would recommend an Epsom salt bath as a replacement for that is quite terrifying, a fine example of dangerous ignorance. While a very strong Epsom salt solution might kill very bacteria if in a shallow wound, a deep wound can put bacteria into the bloodstream that leaves the site in seconds — completely inaccessible to any antibacterial solution. Ironically, as mentioned above, magnesium heptahydrate is actually treatment for the muscle spasms caused by CT — but it can’t prevent the infection via a puncture wound in the first place. BACK TO TEXT
  14. It is now well understood that every microscopic nook and cranny of our skin — indeed, our entire body, inside and out — is thickly populated with an ecosystem of microorganisms, more diverse than any jungle (see We Are Full of Critters). It is also likely that one of the primary functions of these teensy jungles is to maintain a balance of power, where it’s difficult for any organism to dominate. If soaking in salt water kills bacteria, it might kill off the bacteria that normally live on the skin as well. BACK TO TEXT
  15. If you weigh yourself before and after a bath or sauna, you may find a surprising 1-5 pound weight reduction. This fairly obvious effect is presumably due to fluid loss from sweating. The amount is impressive, considering that you may well have consumed fluid at the same time that you were getting rid of it through your sweat glands. However, it’s certainly consistent with the well-known hazard of fainting in that context, which every public hot tub has very clear warnings about. So I think it’s a reasonably safe assumption that we really do sweat a lot in a hot bath! BACK TO TEXT
  16. The sweat is not “sucked” out of you by salty osmosis, thank goodness, but actively excreted by busy, clever cells that systematically squirt out a variety of waste products along with water, regardless of what you are or are not bathing in. This process is entirely mediated by the clever physiology of those glands, and has nothing (known or significant) to do with any fluid in contact with the skin. If there were, people playing in Great Salt Lake or the Dead Sea (which are waaaaaay saltier than any Epsom salt bath) would experience a dramatically greater and more obvious dehydration effect — to the point of being extremely unpleasant and dangerous! They don’t, of course: they just float and have a good time, immune to any vampiric syphoning of fluids from their bodies. BACK TO TEXT
  17. Why do fingers and toes wrinkle in the bathtub? www.LOC.gov. 2009.

    A good quality short article from the Library of Congress “Everyday Mysteries” series about the phenomenon of skin wrinkling or “pruning” in water.

    BACK TO TEXT
  18. Hansen et al. Testing the validity of the Danish urban myth that alcohol can be absorbed through feet: open labelled self experimental study. British Medical Journal. 2010. PubMed #21156749.

    Can you get drunk through your skin? In this MythBusters-style experiment, three adults were “tested” in the office of a Danish hospital: specifically, their feet were submerged in a bowl containting three 700 mL bottles of vodka. It’s hard to tell if the researchers are serious about this, but they obviously had fun doing it! However, the subjects did not become intoxicated, and their blood alcohol levels did not change. They concluded: “Our results suggest that feet are impenetrable to the alcohol component of vodka. We therefore conclude that the Danish urban myth of being able to get drunk by submerging feet in alcoholic beverages is just that; a myth. The implications of the study are many though.”

    Indeed.

    BACK TO TEXT
  19. Singleton, Kenneth B. The Lyme Disease Solution. 2008. p396. BACK TO TEXT
  20. Medical training credentials are not remotely a guarantee of an intelligent opinion, and this demonstrates it beautifully. All it does is show the kinds of ridiculous things that get said about Epsom salts without a shred of evidence or even an intelligible biological rationale. BACK TO TEXT
  21. Eisenkraft et al. Phase I study of a topical skin protectant against chemical warfare agents. Mil Med. 2009. PubMed #19216298. BACK TO TEXT
  22. Waring. Report on Absorption of magnesium sulfate (Epsom salts) across the skin. Unpublished. 2006. BACK TO TEXT
  23. The others had increased urine levels of magnesium, implying that “the magnesium ions had crossed the skin barrier and had been excreted via the kidney, presumably because the blood levels were already optimal.” In other words, whatever magnesium was absorbed into the bloodstream was promptly removed by the body. BACK TO TEXT
  24. When I asked Dr. Waring about publication, she explained “we just haven’t got around to it yet. I hope to do a bit more and then publish with my London colleague.” BACK TO TEXT
  25. Little rant there. It really gets my knickers in a twist when people gripe about science “not knowing everything,” or “there’s other ways of knowing.” As if science doesn’t know it has limits! If scientists thought everything was done, they would stop! Sheesh. BACK TO TEXT
  26. See 2007 Darwin Awards: The Enema Within, in which a man died from an alcohol enema. “In order to qualify for a Darwin Award, a person must remove himself from the gene pool via an ‘astounding misapplication of judgment.’ Three litres of sherry up the butt can only be described as astounding.”

    See also, if you dare, this real news item about a frat boy who almost killed himself “butt chugging” — getting drunk from alcohol injected into the butt. Seriously. “The only thing more embarrassing than almost dying from allegedly butt-chugging is hiring a lawyer to deny it.” No doubt.

    BACK TO TEXT
  27. Dr. Waring has done other research showing that autism is correlated with magnesium deficiency, and her primary reason for studying Epsom salt absorption through the skin was to investigate it as a possible autism treatment BACK TO TEXT
  28. Chestnutt et al. Failure of magnesium sulphate to prevent suxamethonium induced muscle pains. Anaesthesia. 1985. PubMed #4014628.

    In fit unpremedicated patients undergoing minor operations and who were ambulant on the afternoon of the operations, pretreatment with magnesium sulphate given intravenously did not reduce the incidence of suxamethonium induced myalgia below that in a similar series who received no prophylactic therapy. The injection of magnesium in conscious patients is followed by unpleasant side effects.

    BACK TO TEXT
  29. Consider the seminal text, Muscle Pain: Understanding Its Nature, Diagnosis and Treatment. It has nine chapters devoted to nine different kinds of muscle pain. It also doesn’t mention Epsom salts. Not once. BACK TO TEXT
  30. Cell Size and Scale. learn.genetics.utah.edu. 2010.

    A beautiful animated tool for visualizing the scale of cells.

    BACK TO TEXT
  31. Kogler. The analgesic effect of magnesium sulfate in patients undergoing thoracotomy. Acta Clin Croat. 2009. PubMed #19623867. BACK TO TEXT
  32. Lysakowski et al. Magnesium as an adjuvant to postoperative analgesia: a systematic review of randomized trials. Anesth Analg. 2007. PubMed #17513654. The authors of the review concluded: “These trials do not provide convincing evidence that perioperative magnesium may have favorable effects on postoperative pain intensity and analgesic requirements.” BACK TO TEXT
  33. Dr. Waring: “The cytokines released in the inflammatory state actually depress the expression of cysteine dioxygenase, the rate-determining step in the conversion of cysteine to inorganic sulphate. About 80% of the in vivo requirement of sulphate goes through this pathway as sulphate is not well-absorbed from the gut.” BACK TO TEXT
  34. Epsom Salt & Apple Cider Vinegar Treatments Nature's Healing & High Energy Bath. RacingSmarter.com. 2006. BACK TO TEXT
  35. Which actually suggests an interesting point: if modest amounts of Epsom salts in your bath allegedly has therapeutic effects, then it is reasonable to guess that the much higher concentrations of salt used in floatation therapy or found in the famous salt lakes would have a really dramatic effect — perhaps even a toxic effect. But bathing in much higher concentrations of salt has no significant effect at all … other than making people float. BACK TO TEXT
  36. A UK floatation tank manufacturer’s website, floataway.com, admirably restrains itself from extravagant claims of medical benefits, discussing only the benefits of relaxation. As for Epsom salt, the website says it is used “because it raises the density of the water, making it easy to float, and because it has a silky feel which is very good for the skin.” I’m not sure what they mean by “good for,” but I’m guessing it just feels pleasant. BACK TO TEXT