The frequently used term “Epsom salts” is really a misnomer, as there is only one kind of salt in Epson salt. It’s an inorganic salt compound called magnesium sulfate and it’s made up of magnesium (Mg), sulfate (SO4) and seven water molecules. It is named after the English town of Epsom, where a spring “gave forth bitter saline water” containing the compound.
Magnesium is an abundant mineral in the body. It is a cofactor in more than 300 enzyme systems that regulate diverse biochemical reactions in the body, including protein synthesis, muscle and nerve function, blood glucose control, and blood pressure regulation. 
Magnesium is required for energy production, oxidative phosphorylation, and glycolysis. It contributes to the structural development of bone and is required for the synthesis of DNA, RNA, and the antioxidant glutathione. Magnesium also plays a role in the active transport of calcium and potassium ions across cell membranes, a process that is important to nerve impulse conduction, muscle contraction, and normal heart rhythm. 
Epsom salt has been traditionally used as a component of bath salts (the water-soluble, mixture of pulverized minerals that are added to water to be used for bathing, and not the designer psychoactive recreational drugs). It is also used by gardeners to improve crops. People have also used Epsom salt as a home remedy for muscle soreness, bruises and sprains, ingrown toe nails, sunburn pain, tired swollen feet, and joint pain and swelling.
The FDA has approved oral Epsom salt as a laxative for the relief of occasional constipation (irregularity). See section below.
Epsom salt can be purchased in 1 to 8 pound packages of small, colorless crystals. It is available in most pharmacies either in the first aid or bath products sections. To use, add the suggested amount of Epsom salt (usually 1-2 cups) to very warm (not hot) water. Add it as the water is running to help it dissolve. Note: You should not use Epsom salt in a hot tub, whirlpool or jet tub unless the manufacturer permits its use.
Magnesium sulfate can also be used intravenously (although we are not going to talk about these applications in this article as this is not what people buy when they buy Epsom salt). Approved intravenous uses include:
- As replacement therapy for hypomagnesemia (low magnesium in the blood)
- As an antiarrhythmic agent in the special cases of torsades de pointes in cardiac arrest and for managing quinidine-induced arrhythmias.
- As a bronchodilator after beta-agonist and anticholinergic agents have been tried, e.g. in severe exacerbations of asthma. Magnesium sulfate can be nebulized to reduce the symptoms of acute asthma. It is commonly administered via the intravenous route for the management of severe asthma attacks.
- In pregnancy, magnesium sulfate is effective in decreasing the risk that pre-eclampsia progresses to eclampsia. IV magnesium sulfate is also used to prevent and treat seizures of eclampsia. It reduces the systolic blood pressure but doesn't alter the diastolic blood pressure, so the blood perfusion to the fetus isn't compromised.
Is There Any Research?
If you type in the term Epsom salt into PubMed, it comes up with 8688 entries. However, when you begin to look at the entries, the vast majority are talking about magnesium sulfate, used in an intravenous form to treat one of the above conditions. Even if you type in Epsom salt muscle pain, you get intravenous magnesium sulfate articles, many using MgSO4 as adjuvants to anesthesia. Using the terms Epsom salt topical, 37 papers come up. Even among these, only three appear even remotely related to the use of Epsom salt as we are discussing here.
Frustrated, I started to think about that what was really at the crux of the matter. Most of the benefits ascribed to Epsom salt is related to its ability to change magnesium. So, can magnesium even get into the body through the skin in a meaningful way to effect any changes? Unbelievably, there isn’t much research done on this either, but I was able to dig up a few papers which may help us answer that question. They will be discussed below.
Does Epsom Salt Boost Magnesium Levels?
One must assume that to boost magnesium levels in the body by soaking in a tub of water with Epsom salt in it; that the magnesium and/or sulfate ions must have a way to get through the skin. The problem is that skin is designed to be relatively waterproof, so how would magnesium get into the body?
A brief primer on skin
Even at its thickest point, our skin is only a few millimeters thick. But it is still our heaviest and largest organ, making up about one seventh of our body weight: Depending on your height and body mass, it weighs between 3.5 and 10 kilograms (7.5 and 22 pounds) and has a surface area of 1.5 to 2 square meters.
Skin has a lot of different functions. It is a stable but flexible outer covering that acts as barrier, protecting the body from harmful things in the outside world such as moisture, the cold and sun rays, as well as germs and toxic substances.
To be able to do all these things, skin consists of three different layers: the outer layer (epidermis), the middle layer (dermis) and the deepest layer (subcutis). Depending on where it is on your body and the demands made on it, your skin varies in thickness. The outermost layer of skin which you can see is called the epidermis. Its outermost layer, the stratum corneum, is mainly made up of dead cells (keratinocytes) that are firmly stuck together.
It is composed of about 15 to 20 layers of flattened cells embedded in a fatty matrix of ceramides, cholesterol, and fatty acids, which act as a water-repellent barrier. MgSO4 in a water solution is an ionized form and is thereby unable to penetrate this lipophilic (fat-preferred) layer at least by way of absorption.
Skin is somewhat permeable to very small ions. In a paper by Bos and Meinardi, , they argue that the molecular weight (MW) of a compound must be under 500 Dalton to allow skin absorption. A magnesium ion is only a measly 24 Daltons, so it should be no problem. Right? Not so fast.
According to Jahnen-Dechent et al  magnesium binds water tighter than calcium, potassium and sodium. This makes hydrated Mg’s radius ∼400 times larger than its dehydrated radius- and bigger than the 500 Dalton limit.
Back now to Magnesium Absorption
The most frequently (and almost only) cited report on the absorption of magnesium through the skin is by Rosemary Waring . It was done at the University of Birmingham, UK. Nineteen healthy volunteers between the ages of 24 and 64 years, took baths at 50-55℃ into which varying amounts of Epsom salt was added. They stayed in the bath for 12 minutes and took the baths daily at the same time for 7 days.
Blood magnesium levels were obtained before the first bath and 2 hours after the 7th bath. Urine magnesium levels were collected before the first bath and then 2 hours after each bath and 24 hours after the last bath. Their results:
“Of 19 subjects, all except 3 showed a rise in magnesium concentrations in plasma, though this was small in some cases. The values before the first bath were, mean 104.68 ± 20.76 ppm/ml; after the first bath the mean was 114.08 ± 25.83 ppm/ml. Continuation of bathing for 7 days in all except 2 individuals gave a rise to a mean of 140.98 ± 17.00ppm/ml.
Prolonged soaking in Epsom salts therefore increases blood magnesium concentrations. Measurement of magnesium levels in urine showed a rise from the control level, mean 94.81 ± 44.26 ppm/ml to 198.93 ± 97.52 ppm/ml after the first bath. Those individuals where the blood magnesium levels were not increased had correspondingly large increases in urinary magnesium showing that the magnesium ions had crossed the skin barrier and had been excreted via the kidney, presumably because the blood levels were already optimal.”
If you look closely at these results you can see can that even in those with an increase in blood magnesium, the amount is not that much and may not be clinically significant. Also, there are no controls in this study (could the hot water be the deciding factor?) Lastly, this paper was never published in a peer reviewed journal. It is cited on the Epsom Salt Council’s website as their only proof of magnesium absorption. BTW, they also point out that Epsom salt is a go-to craft ingredient for its likeness to fresh fallen snow!
If you assume small amount of magnesium can get through the skin, how does it bypass the 500 Dalton rule? An interesting study by Chandrasekaran et al  took skin that was obtained from patients undergoing tummy tucks. Some samples they exposed to deionized water, others to a 5mM magnesium chloride solution.
In addition, they exposed skin that had the uppermost layers removed by tape stripping it 30 times and lastly, they took some samples and plugged the hair follicles with a kind of “super-glue.” These types of tissues were also subjected to MgCl₂ solution. After treatment, the skin was stained with a dye that “lights up” Mg ions when examined with multiphoton microscopy.
The results show that a small amount of Mg crosses the skin- and the extent depends on the thickness of the stratum corneum (normal vs taped stripped samples).
Note: there is some Mg staining even in samples which were not exposed to MgCl₂ solution. In addition, samples with plugged hair follicles allowed much less Mg absorption than those with intact hair follicles. They conclude that hair follicles act as a major route of penetration of magnesium ions through the skin. It must be noted, however, that hair follicles and sweat glands constitute only 0.1% to 1% of the skin surface.
On the other side, consider this: The Dead Sea is the deepest and saltiest lake on earth. The ocean has a magnesium concentration of approximately 52mM. The Dead Sea’s is closer to 1.9M! Both of these are much higher than the magnesium concentration in an Epsom salt bath.
Shani et al  looked at the penetration of electrolytes through the human skin. They had healthy volunteers as well as volunteers with the skin condition psoriasis bathe in the Dead Sea or a simulated bath-salt solution for 30 minutes. The only significant increases in blood chemistries were seen in the psoriatic patients, and the elevated substances were bromine, rubidium, calcium and zinc (but not magnesium).
In another study, by the Israeli military , looked at a topical skin lotion, called IB1, to protect against chemical warfare agents. IB1 is a hydrophilic water-based solution, composed of magnesium sulfate and glycerin. This was a phase 1 study to assure that IB1 is safe for human to put on their skin.
Fifty human volunteers enrolled in a randomized placebo-controlled, double-blind study were subjected to multiple applications of IB1. Blood and urine magnesium levels were measured and “No detectable levels of the protectant ingredients were found in blood and urine during the entire monitoring period. Also, blood and urine Mg levels were not increased.”
There is little evidence that Epsom salt baths can significantly increase blood magnesium levels. If you have low blood magnesium levels, it would be much simpler and reliable to get additional magnesium either in the diet or by an oral supplement. Foods rich in magnesium include green leafy vegetable, fruit (figs, avocado, banana and raspberry) nuts and seeds, legumes, seafood (salmon, mackerel, tuna), whole grains (brown rice and oats), tofu and dark chocolate.
Does Epsom Salt Ease Pain?
Once again, there is some scientific evidence of the use of intravenous magnesium sulfate used to decrease pain during anesthesia or postoperatively  . But this is not the Epsom salt which we are discussing in this article.
When I did a search of PubMed looking for “Epsom salt muscle pain,” and eliminated those articles dealing with intravenous magnesium sulfate, I was left with nothing! I did manage to find one paper by Engen et al  on the effect of transdermal magnesium chloride on patients with fibromyalgia. Fibromyalgia is a syndrome characterized by chronic pain, fatigue, depression, and sleep disturbances with no known cause.
The study looked at 40 women with a diagnosis of fibromyalgia. They were each provided a spray bottle containing a transdermal magnesium chloride solution and asked to apply 4 sprays per limb twice daily for 4 weeks. Participants were asked to complete the Revised Fibromyalgia Impact Questionnaire (RFIQ), a health survey, and a quality-of-life analog scale at baseline, week 2, and week 4. Only 24 women completed the study, with almost a quarter of the participants who dropped out doing so because of skin irritation.
The researchers found significant improvement in the RFIQ but not on the health survey. The Quality of Life scale showed improvement at 2 weeks but not significant changes at 4 weeks. Oral magnesium (in the form of magnesium citrate) has been found to be helpful in the treatment of fibromyalgia .
Although it might feel good to lie in a warm Epsom salt bath, there is no scientific evidence to support the assertion that topical Epsom salt decreases pain.
Does Epsom Salt Reduce Stress?
There are no studies in PubMed that examine topical Epsom salt’s ability to reduce stress. One website cites a paper by Seelig  as proof that Epsom salt can treat stress. It says that magnesium deficiency can enhance a stress reaction. Based on what we’ve found in the first section, there is little evidence that bathing in Epsom salt can significantly raise blood magnesium levels to a point that it can normalize a magnesium deficiency state.
Once again, diet and oral supplements would be more reliable in this case. Laying in a warm bath with or without Epsom salt may be relaxing, but there’s no way to prove that it’s the Epsom salt that makes it so.
There is no scientific evidence that Epsom salt reduces stress.
Does Epsom Salt Help Eliminate Toxins?
Detox proponents say the body is under constant assault from toxins such as smog, pesticides, artificial sweeteners, sugar, and alcohol. Without a periodic cleansing, these poisons accumulate in the body and cause headaches, fatigue, and a variety of chronic diseases. A variety of “detoxification” (“detox”) diets and regimens—also called “cleanses” or “flushes”—have been suggested as a means of removing toxins from your body or losing weight. Detoxification may be promoted in many settings and may also be used in naturopathic treatment.
“But the science behind the detox theory is deeply flawed“, says Peter Pressman, MD, an internal medicine specialist at Cedars-Sinai Medical Center in Los Angeles. “The body already has multiple systems in place — including the liver, kidneys, and gastrointestinal tract — that do a perfectly good job of eliminating toxins from the body within hours of consumption.”
The National Center for Complementary and Integrative health agrees, saying “There isn’t any convincing evidence that detox or cleansing programs actually remove toxins from your body or improve your health.”
There are no scientific papers that study Epsom salts in eliminating toxins. As previously mentioned, the skin is a water-tight protector of harmful substances. The skin is a one-way defense system; toxins are not eliminated in perspiration.
There is no scientific evidence that Epsom salt can eliminate toxins.
Does It Relieve Constipation?
The FDA has approved Epsom salt as a laxative for the relief of occasional constipation (irregularity). It generally produces bowel movement within 30 minutes to 6 hours. The directions, dosages, and warnings are as follows:
- do not exceed recommended daily dosage
- drink a full glass (8 ounces) of liquid with each dose
- may be taken as a single daily dose or in divided doses
- dissolve the dose in 8 ounces of water. lemon juice may be added to improve the taste.
- adults and children 12 years and over - 2 to 6 level teaspoons (10 to 30 grams) daily
- children 6 to under 12 years - 1 to 2 level teaspoons (5 to 10 grams) daily
- children under 6 years - consult a doctor
Ask a doctor before use if you have:
- kidney disease
- a magnesium-restricted diet
- abdominal pain, nausea, or vomiting
- noticed a sudden change in bowel habits that persists over a period of 2 weeks
- already used a laxative for a period longer than 1 week
Epsom salt can be used in the treatment of constipation. Use as above and be mindful of the above warnings.
Does It Improve Blood Sugar Levels?
As in the sections above, the only evidence of an effect of magnesium sulfate on blood sugar deals with intravenous MgSO4. Although low magnesium may be associated with an increased risk of diabetes , soaking in a tub of Epsom salt is not going to treat your low serum magnesium level. Taking Epsom salt orally might help, if you don’t mind the diarrhea (see the section above). Better to stick with dietary Mg or Mg supplements.
There is no evidence that Epsom salt can improve blood sugar levels.
Is Epsom Salt Safe?
Overall, Epsom salt is a safe, well tolerated material, especially when used as a bath supplement. A little more caution should be used if taken orally.
Common Side Effects of Magnesium Sulfate:
- Upset stomach
Serious Side Effects of Magnesium Sulfate:
- Signs of an allergic reaction (rash; hives; itching; breathing difficulties; chest tightness; or swelling of the mouth, face, lips, or tongue)
- Dizziness, flushing, or faintness
- Irregular heartbeat
- Muscle paralysis or muscle weakness
- Severe drowsiness
Patients with kidney disease should consult their physician before using MgSO4 products. People taking antibiotic medications--for example, demeclocycline, ciprofloxacin or nitrofurantoin--shouldn't take Epsom salts until cleared by a physician. The same is true for patients taking digoxin or digitalis, a cardiac medication. Finally, pregnant women should consult their obstetrician if they're considering taking Epsom salts.
Never use a higher dose of Epsom salt than what is recommended.
Despite being recommended for a variety of ailments, there is surprisingly little scientific research to support the use of Epsom salt for anything other than occasional constipation. As it is a relatively safe substance, go ahead and enjoy a warm Epsom salt bath. Just don’t expect it to cure all that ails you.