Topical Magnesium Sulfate (Epsom Salts baths): its
effectiveness in question.
Jose Mahfoud, ND, MSc
MgSO4 is used in
medicine both orally and intravenously, and it certainly has concrete effects
through these routes. Intravenously it
is used in the treatment of preeclampsia and as a tocolytic; orally it acts as
an osmotic laxative. It is also very popular as a folk remedy for treating
musculoskeletal pain, and for removing “toxins” from the body. When challenging
the validity of traditional remedies one often encounters resistance from some members
of the Alternative Medicine community (both professionals and patients), who
sometimes feel very strongly about certain topics, being one of them the topical
use of MgSO4 (Epsom Salts baths) for the relief of musculoskeletal
pain and the popular concept of “detox”.
No adequate studies have been published
regarding MgSO4 and its transdermal delivery. Most sources that claim Magnesium is
systemically absorbed through the skin lack scientific basis and their
statements are anecdotal. One small
study is found to be repeatedly referenced by supporters of Magnesium
transdermal delivery, some of which also claim that it is best achieved by
applying “Magnesium Oil”, which is not truly an oil but a
saturated aqueous solution of Magnesium Chloride (MgCl2), which
behaves in a similar manner as Magnesium Sulfate in terms of dissociation.
MgSO4 is a white crystalline
substance, highly soluble in water and alcohol but insoluble in oil, with a
molecular mass of 120.366 g/mol (1
g/mol is equivalent to 1 Da). Like
other salts, when dissolved in water it dissociates in Mg+2 and SO4-2. Similarly, Magnesium Chloride dissociates
into Mg+2 and 2Cl. Dissociation
in an aqueous solution occurs when water molecules bind to each of the ions
that form the original substance, therefore breaking apart the crystalline
form. If we were to dehydrate this
solution, the ions once again form bonds between each other, reconstituting the
salt crystal.
Therefore, an aqueous solution
of Epsom Salts makes it nearly impossible for Mg-2 to cross the
epidermal layer, due to its necessary bond with water molecules and, as we
know, the stratum corneum is largely impervious to water, but highly permeable
to oils. Magnesium sulfate is not
liposoluble, hence no transdermal absorption of the compound (nor its ions)
occurs. It lacks two of the three
conditions necessary for a drug to be absorbed through the skin. If any magnesium were in fact absorbed
through the skin the amounts would be negligible, with no perceivable effect.
For a drug to have good
transdermal delivery, it must be:
- of low molecular mass (<500 Da)
- highly liposoluble
- potent enough [low required daily dose (<2 mg)] [1]
The analgesic (and often
spasmolytic) effect attributed to topical MgSO4 is most likely due to the
vasodilating and relaxing effects of heat (warm water)or, even perhaps, the
placebo effect. If it were that easy for
magnesium to be absorbed transdermally, one can infer that sodium (as NaCl) in
sea water would be similarly absorbed (if not more, due to sodium’s smaller mass
compared to magnesium) every time we go for a swim. Such instance would be highly detrimental to
one’s health, especially due to sodium’s well known effects on blood pressure.
Magnesium is best obtained
orally, mainly from foods like almonds, spinach, cashews, beans, etc., which
provide a good (bioavailable) source of the mineral. Nutritional supplements
may also be used should they be indicated to treat deficiency, or if dietary
intake is deemed insufficient.
[1] Transdermal drug delivery:
principles and opioid therapy. Lyn Margetts, FRCA and Richard Sawyer, FRCA FIPP. http://ceaccp.oxfordjournals.org/content/7/5/171.full
Accessed 8-7-2014
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