Love Epsom salt baths? Here's how they affect your body, according to science

For centuries people have soaked in Epsom salt baths to ease aching muscles and relieve stress. But it may be more popular than ever these days with people dumping scoops of the salt into their tubs and splashing photos of it all over social media. Epsom salt is affordable, widely available, and big business. Estimates value the global market at several billion dollars a year—and growing rapidly.

But when it comes to the science behind Epsom salt’s purported health benefits, there are more questions than answers.

”Warm baths alone have benefits with aches and easing tension,” says Jesse Bracamonte, a family medicine specialist with the Mayo Clinic in Arizona. “Whether Epsom salt improves this is yet to be fully understood due to a lack of research and evidence.”

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What about the other claims, such as replenishing your body’s levels of magnesium, killing off harmful bacteria, and its use as a laxative? Here’s what experts have to say.

What is Epsom salt—and what are its supposed benefits?

Legend has it that farmers near the English town of Epsom were alerted to unusual local waters more than four centuries ago because their livestock refused to drink from certain natural springs.

It turned out that these waters were filled with a compound of magnesium and sulfates that would come to be known as Epsom salt. Unlike table salt, a flavor enhancer, Epsom salt produces a bitter and unpleasant taste.

People soon found sitting in the spring waters was relaxing, and the practice turned the area into a spa destination. Epsom salt was extracted from the waters as a standalone product in the late 17th century.

The basic theory of Epsom salt's effectiveness suggests that magnesium and sulfate dissolve in warm water, so that bathers can absorb them through the skin, or inhale them in steam, and take them into the body.

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Magnesium, our body’s second most abundant mineral after calcium, is needed for healthy muscles and nerves, the heart, and to regulate blood pressure. It’s sourced from foods like greens, nuts, and beans, but many people don’t get their recommended daily amounts of magnesium. That can lead to muscle pains, fatigue, stress or other ailments.

Many proponents of Epsom salt baths believe they help to restore the body’s levels of magnesium. 

Do Epsom salt baths really work?

Though there is a lot of debate, there is no definitive scientific evidence suggesting humans can absorb such a significant amount of magnesium through the skin, as in an Epsom salt bath.

Nicholas Theodosakis, a dermatologist at Massachusetts General Hospital and Harvard Medical School, says he’s never seen any controlled study suggesting soaking in Epsom salts has such a benefit—or any real benefit at all.

“My take, as someone who does biochemistry and dermatology for a living, is that it doesn’t make a lot of sense,” he says. “The skin is mostly a barrier, not a sponge. People like me who develop drugs for topical use spend so much time and energy trying to get stuff through the skin because it’s so darn hard.”

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Theodosakis adds that those who hope to replenish their magnesium levels would probably find it more efficient to source it though food or the oral supplements on the market. “The gut is designed to absorb things,” he says, “it’s kind of the opposite of the skin in that way.” 

Nonetheless, many people do indeed report that soaking an Epsom salt bath helps to relax their muscles, relieve pain, and make them feel less stressed. But maybe it’s not because of magnesium. The hot soak itself boosts blood flow and helps to loosen and relax both muscles and joints. A warm bath can also temporarily lower blood pressure and help you relax—whether Epsom salt is involved or not.

Theodosakis is also skeptical of bathers’ claims that Epsom salt can kill off harmful bacteria and fungus on the body. “I’m not aware of any studies that have really rigorously evaluated Epsom salt for changing levels of bacteria,” he notes, “and I strongly suspect a diluted salt, at the levels you’d put into a bath, is not going to have any major effect.”

Can you take Epsom salt as a laxative?

Epsom salts are also promoted as a laxative, approved by the U.S. Food and Drug Administration. While other laxatives may be more effective, and produce fewer side effects like bloating, consuming Epsom salt dissolved in water can ease occasional constipation when used as directed and in suggested doses. But be wary of ingesting too much—if you can get past the taste to try.

In recent years scientists have identified the bitterness receptor in our taste buds that reacts to Epsom salt and warns the body not to ingest too much of a substance that could prove toxic. Ingesting excessive amounts of magnesium salts can cause severe vomiting and diarrhea, or even a drop in blood pressure and cardiac arrest, although none of these side-effects are threats to bathers.

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Epsom salt functions as a laxative by pulling water from the body to help flush out the gastrointestinal system, but Bracamonte says it may not be the best tool for the job. “There may be more options available that have better evidence,” he notes. Those include other magnesium-based laxatives like milk of magnesia or magnesium citrate.

Is Epsom salt safe?

Although a lack of scientific study does cast some doubt on Epsom salt’s time-honored healing properties, ultimately there is no doubt that many people do find that soaking in a hot bath with Epsom salt makes them feel better. On that point, experts seem to agree, there’s no real reason not to indulge. 

“Other than a really rare circumstance, like where you might have a lot of open wounds, I don’t think there’s really any harm that I’m aware of,” Theodosakis says. “I tell people, ‘if you enjoy it, then go for it.’”