While clearing out my in-laws’ old house, I realized how easy it is for all kinds of junk to accumulate over time. Was a bag of Epsom salts, for example, worth keeping? I'd heard that a warm bath with Epsom salts relieves sore muscles and wondered if it really made a difference. I was plenty sore from moving and removing forty years of stuff, so I thought I’d try it out.
The warm bath was pleasant enough, but I did not notice any particular effects beyond taking a regular bath. Maybe it was just me, so I looked for some evidence of the effectiveness of Epsom salts.
Epsom salt is a singular compound called magnesium sulphate. Back in 1695, Nehemiah Grew patented the name Epsom salts for "bitter purging salts" found in Epsom, England. They are still taken internally as a laxative, but I wanted to know about its usefulness in a bath. Henry Wicker set up the first spa in Epsom in the early seventeenth century after he noticed his cows would not drink the water of a natural spring. The Saltworks web site claims, "An Epsom salt bath is known to ease pain and relieve inflammation, making it beneficial in the treatment of sore muscles, bronchial asthma and migraine headaches." And the Epsom Salt Council site asserts, "Doctors, celebrities, personal trainers, gardening experts and supermodels have all extolled its virtues." Despite the unspecified endorsement of such scientific authorities as celebrities and supermodels, I could not find any evidence that adding Epsom salts to a bath does any good for aches and pains.
Sites advocating the use of Epsom salt for bathing, seem to assume its effectiveness and then provide some speculations on why it might work, mentioning how Magnesium is an important trace element in the body, playing significant roles in bones and many physiological processes. Apparently, many people might be lacking in Magnesium and adding some to your system must be a good thing. Taking a bath in the stuff doesn't seem like a very efficient strategy because skin does not easily absorb materials. The Epsom Salt Council quotes an unpublished paper by a toxicologist that magnesium levels rose after taking a very hot bath with Epsom Salts, although this study did not control for the effect of taking a normal bath. And the usefulness of increasing magnesium levels in the blood in relation to muscle aches is unclear.
Osmosis involves moving water molecules from one side of a permeable membrane to another. Even if this were happening (and no evidence was shown that it was) the relevance to muscle pain is unclear. You would need a higher concentration than indicated, and if removing fluid were relevant to the problem, then other kinds of salt would also work.
One of my problems with culling things and ideas is that I'm never totally sure about how I feel about them. So if you have any good evidence for the usefulness of Epsom Salt in a bath, by all means, add them to the comments below.
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