Epsom salts are magnesium sulphate heptahydrate, usually shortened just to magnesium sulphate.
In water, it breaks down into magnesium and sulphate. The theory (and widespread confidence) is that when you soak in an Epsom salt bath, these get into your body through your skin and basically most of Epsom salts’ beneficial properties (listed at the bottom of the page) based on the idea of absorption of the minerals through the skin.
While the conventional wisdom has been challenged by some recent research, no one bloody knows how this actually works. How magnesium penetrates through skin which by definition supposed to be protective and waterproof?
True, the top layer of the skin, the stratum corneum, consists of dead cells packed with a kind of embalming substance, a fibrous protein known as keratin. Water definitely can’t go through or around them, thanks to a microscopic “uniquely structured fatty layer” between them, which no one knew about until surprisingly recently (2012 study). Plus we have glands that coat the skin in waterproofing oils. When those oils wash off, the dead skin cells can soak up a little water and swell a bit, like soaked beans.
Our skin is not a perfect barrier to all substances - medicinal patches and creams, allergic reactions, contact poisons and other examples that some things clearly do get past that dead outer layer to interact with the living cells beneath, even into the blood stream. The skin keeps water and much else out, but some things get through. If molecules are small enough, they can slip through the skin. What?!
In 2000, Bos and Meinardi argued that a teensy enough molecule, smaller than 500 Daltons, can drift through the corneum — the 500 Dalton rule (virtually all common contact allergens are under 500 Dalton, same as most commonly used pharmacological agents applied in topical dermatotherapy and all known topical drugs used in transdermal drug-delivery systems).
There are almost certainly other mechanisms involved. For instance, cells in the living layer of the skin take an active role in managing the passage of some substances. Topical allergic reactions are an obvious demonstration of this: the immune system over-reacts to an “invader.” The 500 Dalton rule means that it’s plausible in principle that magnesium ions might diffuse through the stratum corneum.
Like this study performed in 2016 found that:
• “topically applied magnesium permeates through human stratum corneum”
• “magnesium permeability varies based on concentration and time of exposure”
• “hair follicles have significant contribution towards magnesium penetration through skin”
Further more. In 2006, Rosemary Waring, a British biochemist at the University of Birmingham, did an experiment with Epsom salts. She measured magnesium and sulphate in the blood and urine both before and after people bathed in Epsom salts. She found them to be higher after the baths!
16 out of 19 people had more magnesium and sulphate in their blood after the baths than they did before the baths. Waring’s results are straightforward. No therapeutic effects of Epsom salt were studied or claimed — she just studied absorption. While experiment hasn't yet actually been published and being a basic rule of science that evidence can’t really be taken too seriously until it has been exposed to peer review and repeated by other scientists. Still just because experimental results haven’t been replicated yet doesn’t mean we should ignore them.
So what can we make of Dr. Waring’s results? One thing for sure…
There might be a mechanism for getting magnesium and sulphate across the skin!
Regardless whether magnesium or sulphate can penetrate and do its magic there's other reason to put Epsom salts in your bath. Once dissolved in your bath it does make the water feel nice. No research is required to prove that: just try it! Most people agree that the water feels smoother, slicker, silkier. It sounds lovely, right?
Here are some commonly claimed properties and benefits of Epsom salts.
Anti-bacterial: Epsom salts can be an effective treatment for topical skin infections, as salt is certainly inhospitable to many microganisms - basically any strong salt solution is anti-bacterial.
Hangover cure: Hangovers are caused by the toxicity of the alcohol breaking down in the body. The byproducts of this - dehyratation - a trigger of throbbing headache, fatigue and nausea. The sulphates in Epsoms salt help flush out toxins and ease muscle pain.
Magnesium source: Epsom salts will boost your skin’s magnesium level.
Recovery: A long soak will help with aches, stiffness, tightness and soreness after exercise.
Try to take Epsom salts bath after a long-haul flight - that will have a sedative effect on the body or Epsom salts foot soak to soothe aches and pains after a day in heels - to reduce swelling and puffiness.
Rejuvenating & detoxifying: Rubbing the skin with Epsom salts removes dead skin cells and promotes healing and rejuvenation as well as removing toxins.
Massage handfuls of Epsom salts over wet skin, starting with the feet and working upwards towards the face. Then have a bath to rinse. Post-scrub, your skin will look luminous, smooth and soft and will better absorb skincare products.
Relaxant: The minerals help muscles and joints to relax and this leads to a more restful sleep, giving the body a chance to re-energise. Many athletes take a soak the night before a race.