Do you love Epsom salt baths? This is how science says they affect your body

For centuries, people have taken Epsom salt baths to relieve muscle pain and reduce stress. But today, it’s perhaps more popular than ever: people are pouring the salt into their tubs by the spoonful and posting photos of it on social media. Epsom salt is affordable, widely available, and big business. The global market is estimated to be worth billions of 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 help with pain and relieve tension,” says Jesse Bracamonte, a general practitioner at the Mayo Clinic in Arizona. “Whether Epsom salts relieve this is not yet fully understood due to a lack of research and evidence.”

(We’ve swapped bathtubs for showers – but which is better for you?)

And what about the other claims, like that it replenishes the body’s magnesium levels, kills harmful bacteria, and acts as a laxative? Here’s what experts have to say.

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

According to legend, farmers near the English town of Epsom became aware of unusual waters more than four centuries ago because their livestock refused to drink from certain natural springs.

It turned out that this water contained a compound of magnesium and sulfates that became 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 water relaxing and turned the area into a health resort. In the late 17th century, Epsom salt was extracted from the water as a separate product.

The basic theory behind the effectiveness of Epsom salt is that magnesium and sulfate dissolve in warm water, allowing bathers to absorb them through the skin or inhale them in the form of steam and absorb them into the body.

(How magnesium affects your sleep and anxiety.)

Magnesium is the second most abundant mineral in our bodies after calcium and is needed for healthy muscles and nerves, the heart and to regulate blood pressure. It is found in foods such as vegetables, nuts and beans, but many people do not consume the recommended daily amount of magnesium. This can lead to muscle pain, fatigue, stress or other ailments.

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

Are Epsom salt baths really effective?

Although there is much debate about this, there is no clear scientific evidence that humans can absorb as much magnesium through the skin as they can from an Epsom salt bath.

Nicholas Theodosakis, a dermatologist at Massachusetts General Hospital and Harvard Medical School, says he has never seen a controlled study suggesting that an Epsom salt bath has such benefits — or any real benefits at all.

“In my opinion, as someone who does biochemistry and dermatology professionally, that doesn’t make a lot of sense,” he says. “The skin is primarily a barrier, not a sponge. People like me who develop topical drugs spend so much time and energy trying to get things through the skin because it’s so damn difficult.”

(Vitamin C, retinol, biotin? This is what your skin really needs.)

Theodosakis adds that those looking to replenish their magnesium levels would likely find it more efficient to get it through food or the oral supplements on the market. “The gut is designed to absorb things,” he says, “so it’s kind of the opposite of the skin in that respect.”

Still, many people actually report that an Epsom salt bath relaxes their muscles, relieves pain, and makes them feel less stressed. But maybe it’s not the magnesium. The hot bath itself increases circulation and helps loosen and relax 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 salts can kill harmful bacteria and fungi in the body. “I’m not aware of any studies that have really thoroughly examined Epsom salts for changing bacterial levels,” he notes, “and I strongly suspect that diluted salt in the amount you would put in a bath isn’t going to have much of an effect.”

Can you take Epsom salts as a laxative?

Epsom salt is also promoted as a laxative and is approved by the U.S. Food and Drug Administration. While other laxatives may be more effective and cause fewer side effects such as bloating, consuming Epsom salt dissolved in water may relieve occasional constipation when used as directed and at the recommended dosage. But be careful about taking too much of it—if you can get past the taste, give it a try.

In recent years, scientists have identified the bitter receptor in our taste buds that responds to Epsom salts 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 dangerous to bathers.

(Castor oil is also a laxative – but it is not a cure-all, as some claim.)

Epsom salts work as a laxative by removing water from the body and flushing out the gastrointestinal system. However, Bracamonte says it may not be the best option for this. “There may be other options that have better evidence,” he notes. These include other magnesium-based laxatives such as milk of magnesia or magnesium citrate.

Is Epsom salt safe?

Although there are doubts about the time-tested healing powers of Epsom salts due to a lack of scientific studies, there is ultimately no doubt that many people find that a hot bath with Epsom salts makes them feel better. On this point, the experts seem to agree that there is no real reason not to treat yourself.

“Other than really rare circumstances, like if you have a lot of open wounds, I don’t think it’s really harmful, as far as I know,” says Theodosakis. “I tell people, ‘If you enjoy it, then do it.'”