There's No Proof Epsom Salt Baths Actually Do Anything
The folk remedy could even make your muscle problems worse.
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Long before Calgon ever pushed the teleportation powers of bubble baths—just Google it, okay?—humans have hit the tub for relief from their aches and pains.
And in wisdom passed down from generation to generation, stirring in some Epsom salts is supposed to increase the healing effects of water. A 12-minute soak in a magnesium sulfate solution, the package in my bathroom cabinet promises, infuses rich minerals through the skin to relieve sore muscles.
The only trouble? There's really no evidence to support this claim, at least according to experts in muscle health. Physical therapist John Cavanaugh of the Hospital for Special Surgery in New York City, for instance, says that in more than 30 years of treating sports injuries, he's never once administered or recommended an Epsom salt soak. In his search of the scientific literature, he can't track down a single study showing any benefit.
Epsom-salt baths might make people in pain feel a little bit better psychologically, says Naresh C. Rao, a sports medicine physician who treated Olympic water polo players at the 2016 Summer Games in Rio. But he also acknowledges the complete and total lack of data to support them.
Researchers, however, haven't ever truly tackled the issue, either, aside from one small British experiment involving daily baths for a week in scalding-hot water that's never been peer-reviewed or published in a journal. For one thing, they're busy studying slightly more significant questions, such as how to treat muscular dystrophy, says Matthew Hudson, director of the Integrative Muscle Physiology Lab at Temple University.
There's the fact that they likely already know the answer to the question of whether these soaks really work. "Based on biochemistry and physiology, the theories around how Epsom salts reduce muscle pain are likely untrue," he says.
The main mineral in question—magnesium—does play a role in regulating muscle contractions, and low levels have been known to cause spasms or seizures. Pregnant women receive high doses of magnesium sulfate by mouth to treat seizures caused by a dangerous condition called preeclampsia.
But administering magnesium sulfates intravenously failed to reduce muscle pains in one small study performed back in the 1980s. And a research review found little evidence that magnesium salts, taken either orally or through IV, eased nighttime muscle cramps.
Even if delivering a magnesium solution into your body worked, your skin is a relatively waterproof tissue designed to protect you from your surroundings, Hudson points out. "If you are extremely dehydrated you can't rehydrate by dipping your leg or arm into water, and you won't get intoxicated by dipping your arm into a barrel of wine," he says.
Some proponents cite the idea of "osmosis" to explain how magnesium can penetrate the skin. That term actually refers to the movement of a solvent like water across a permeable barrier, not the substance (called a solute) that dissolves within that solvent. The idea is that water moves from an area in which there is a lower concentration of solute into one with a higher concentration to create a more balanced solution.
"For example, if you put salt on a slug they shrivel up and die," Hudson says. "This occurs not because the salt enters the slug and kills them, but because the salt causes the water to exit them via osmosis."
When it comes to baths, the temperature of the water has a far bigger effect on your body than anything you might mix in, Hudson says. And here's where Epsom salt baths—especially warm ones—might hinder, rather than help, healing.
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Apply heat too soon after an injury like a sprained ankle or a torn muscle and you might exacerbate the damage by widening blood vessels and boosting the flow of pro-inflammatory compounds, Cavanaugh says.
That's why health care providers usually reach for ice first—to constrict blood vessels and to slow down cellular metabolism around the site of your injury. When chilled, "your tissue doesn't require as much oxygen, and cells don't necessarily die a secondary hypoxic death from the effusion and swelling," he says.
After your swelling's subsided or if you're dealing with chronic issues like back pain, heat can sometimes reduce tension and promote relaxation. Rao says he sometimes uses warm baths, Jacuzzis, or moist heating pads to treat athletes, and notes that hot soaking tubs were available for Olympians in Rio, though they didn't have Epsom salts.
However, hot baths can increase your heart rate and drop your blood pressure, which might be dangerous for people with cardiac conditions, Cavanaugh says. So check with your doc first if you have heart issues. Beware mix-ins if you have sensitive skin, a magnesium sulfate allergy, or broken skin. Rao had one patient develop a burn-like rash from Epsom salts.
And one last consideration, at least when it comes to that can't-lift-your-arm feeling a day or two after the gym: "Recent research indicates that muscle pain following exercise is actually beneficial and part of how muscle adapts and becomes stronger from exercise," Hudson says. In other words, do too much to ease soreness and you might actually reduce your gains. Ouch.
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