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QQs: Do Epsom salt baths do anything?

If you've ever felt achy after a long run or had a stubborn ingrown toenail, you might have read online about the wonders of Epsom salt. Sprinkle some into a bath, take a long soak, and voila, you're on your way to feeling better.

Besides softening your skin and relieving pain, some people even claim that Epsom salt can somehow raise your mineral levels or draw toxins from your body, whatever that means. But like most things on the internet, it's probably too good to be true.

Epsom salt is a form of magnesium sulfate, a compound made of magnesium, sulfur, and oxygen. It was named Epsom after a small town in Surrey, England, which is just southwest of London. In the 1600s, it became a popular spa town because some of its natural springs were full of magnesium sulfate.

Most of the claims about Epsom salts solving your life's problems have to do with the magnesium in it. Your body uses magnesium to carry out all kinds of chemical reactions, and it also helps to keep your bones strong, your nerves firing properly, and your heart beating consistently. Which are all probably things you want. There's just one problem. There's no evidence that any of the magnesium in your Epsom salt bath actually gets inside you.

One report did show magnesium and sulfate levels going up in people's blood after they soaked for a few minutes in an Epsom salt bath, but the study didn't have a control group for comparison, and it was never published in a peer-reviewed journal. So they aren't the most reliable results in the world. You might even say that you should take them with a giant grain of salt.

The truth is your skin is a great barrier, and it doesn't just absorb anything that's touching it, so most experts don't think that much, if any, of the mineral gets into your body during a soak. But even if some did, that magnesium would only help people who have a deficiency. If you already have enough magnesium, more isn't going to help you. And if you do have a deficiency, there are much better ways to get extra magnesium, like through certain nuts and leafy veggies.

Now that doesn't mean that magnesium sulfate isn't a useful drug. When you drink it, it's actually a well-known laxative, and injected, it can help prevent pregnant women with high blood pressure from having seizures. It's pretty amazing. But that relief your sore muscles get from a bath? It's possible the salt is doing something, but it's more likely that it's a placebo: you think it should help, so you feel like it does. The benefits could also be from the warm water and the relaxing feeling of the bath itself,  with no salt necessary.

Until a well-designed study tests it out, we won't know for sure, but there's a good chance Epsom salt baths aren't any better than a plain old tub of water. That said, Epsom salts aren't harmful, so even if they aren't doing anything for you, if you like taking your Epsom salt baths, you can keep doing that. Just don't say that there's any scientific proof that they work.

Thanks to Pateron patron Elizabeth Harrity for asking this question. And thanks to all of our patrons who keep the answers coming. If you'd like to help support the show and submit your questions, you can go to patreon.com/scishow. And for more episodes like this, you can go to YouTube.com/scishow and subscribe.

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