SaveYourself.ca • Sensible advice for aches, pains & injuries
published 10/26/06, updated 8/26/11
Welcome to what is — oddly — the most popular article on the internet about Epsom salts. In the last year, this page has become the dominant source of information about Epsom salts online. Apparently, I have written more about this subject 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.”
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 serious article.
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. Note that “relieves pain” and “speeds healing” are as different as a flying dream and actually flying.
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 that 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. 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.”1
No evidence for the efficacy of Epsom salts was ever presented, nor did it seem necessary to talk about it.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.2 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.3 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?
This educational website offers more than 400 free articles about pain problems, but it is also partially funded by the sale of e-books for people with pain problems. If you are researching Epsom salts because you have frustrating muscle pain, please also read the free introduction to this book, which is by far the most advanced self-help guide on this topic published anywhere:
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. 230 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.
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.4 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. Is there any plausible way that Epsom salts could have an effect on your muscle tissue, or on the healing of injuries?
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.)
So, however Epsom salts get into the body — and they probably do, more about this below — 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.14 But Epsom salts do not increase that.15)
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.”16
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 2010.17 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.
I was wrong.
In 2006, Rosemary Waring, a British biochemist at the University of Birmingham, did a nice science experiment with Epsom salts.18 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
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.19 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 six years later, neither experiment has yet actually been published,20 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 …
It’s not much, but it’s important. And when I found the new evidence, I changed my mind. (That’s how science works. That’s why being anti-science is like being anti-honesty.21 I happily admit that Dr. Waring’s results probably mean that I was simply dead wrong about the absorption question originally. I was actually so pleased to be wrong that I wrote an article summarizing this situation and talking a little about what a pleasure it is to be wrong about something in science.)
How does it work, this crossing of the skin? 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.)
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, 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.23
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.”24 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.
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.25
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 simultaneous 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.
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.”
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.”
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 scale26 — 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.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.27 However, this is uncertain science. Several studies have been done, with conflicting results. Most were reviewed in 2007:28 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 reducing pain, but 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!
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.29
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.
Obviously non-salty baths have some benefits of their own. Epsom salts routinely get the credit for these benefits. It goes like this:
Tricksy, the human mind is.
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].30
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 demontrate 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.
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.31 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.32 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.
I can do no better in defense of Epsom salt bathing for aches and pains than “anything is possible.” There is no good or particular 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.
On the bright side, thanks to Dr. Waring, we now know that we are a living experiment in absorbing magnesium sulphate ions every time we bathe in dissolved Epsom salts! And maybe they do something. 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!”
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):
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. 230 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:
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.
See also the Wikipedia article magnesium sulfate (Wikipedia). BACK TO TEXT Comments: “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 Comments: 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 Comments: 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.”
Abstract:BACK TO TEXTIn 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 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
