Magnesium Sprays, Oils, Flakes and Epsom Baths: The Skin Studies

Two human studies have tested magnesium applied to the skin, and none has shown that a spray, oil, cream or bath raises the body's magnesium: the only review, published in 2017, called the claims made for sprays, flakes and salt baths scientifically unsupported; a 25-person trial of a magnesium cream found no significant change in blood magnesium after two weeks; and the one spray study had no comparison group.^{1, 2, 3} Magnesium oil and bath flakes are magnesium chloride, Epsom salt is magnesium sulphate, both bath products rather than food supplements. This page sits inside the Wellgard vitamins and minerals guide.

Can magnesium be absorbed through the skin? What the 2017 review found

The review, in Nutrients, evaluated the published literature on transdermal magnesium and concluded that "the propagation of transdermal magnesium is scientifically unsupported".¹ Its argument, set out in the full text, rests on how skin is built. The outer layer, the stratum corneum, is about 15 to 20 layers of dead, flattened cells set in a matrix of fats, built to keep water in and foreign substances out; only fat-soluble substances cross it in meaningful amounts, and magnesium in a spray or a bath is a charged ion wrapped in a shell of water.¹ The review notes one laboratory study in which magnesium ions did penetrate the stratum corneum, mainly through hair follicles, and puts follicles and sweat glands at 0.1% to 1% of the skin's surface; dead cells carry none of the transporters living cells use to take magnesium in.¹ Two reports often quoted online, a hair-analysis study of a spray and a week of Epsom baths, were never published in an indexed journal; the review calls them of "questionable quality", so no figure from either appears here.¹

What did the magnesium cream trial find?

The one placebo-controlled human study is a 2017 pilot from the University of Hertfordshire. Twenty-five adults, average age 34, were randomly assigned to a cream delivering 56 mg of magnesium a day or a placebo cream for two weeks, with blood and 24-hour urine magnesium measured at the start and at day 14.² Serum magnesium in the cream group went from 0.82 to 0.89 mmol/L, a change the authors call clinically relevant but which was not statistically significant (p = 0.29); the placebo group moved from 0.77 to 0.79. The rise reached significance (p = 0.02) only in a subgroup of non-athletes, and urinary magnesium rose slightly, also not significantly (p = 0.48).² Three facts frame the result: the trial was single-blind and small; the 56 mg a day is, in the authors' words, "a low dose compared with commercial transdermal Mg2+ products available"; and one author may receive royalties on a different, stronger magnesium cream.²

What did the magnesium spray study find?

A 2015 feasibility study at a US fibromyalgia clinic enrolled 40 women with the diagnosis and gave each a spray bottle of magnesium chloride solution, four sprays per limb twice a day for four weeks. Twenty-four completed it, average age 57, and their Revised Fibromyalgia Impact Questionnaire scores improved at weeks 2 and 4 (total score p = 0.001).³ There was no placebo or comparison group, no blood or urine magnesium was measured, and 16 of the 40 dropped out, so the study cannot say what changed the scores. The authors call the result preliminary.³

Do Epsom salt baths raise your magnesium?

No published, indexed study has measured it. The university report that circulates online was never peer-reviewed; the 2017 review is the only indexed paper to discuss it, and it does so to question its quality.¹ So the figure for how much magnesium a bath delivers is: not measured. What Epsom salt is can be stated: magnesium sulphate heptahydrate, about 10% magnesium by weight calculated from the formula, sold as a bath product. The same compound is also a medicine: by injection or infusion it is a hospital medicine, for severe acute asthma among other uses.⁹ That is not a bath, and a bath product is not for swallowing; the medicines that interact with magnesium are in what you should not take with magnesium.

What are magnesium oil and magnesium flakes made of?

Both are magnesium chloride. "Magnesium oil" contains no oil: it is a concentrated brine of magnesium chloride in water that feels slippery because of the salt. Flakes are the same compound as a solid, magnesium chloride hexahydrate, about 12% magnesium by weight calculated from the formula. Chloride is well absorbed when swallowed: in a 2001 human comparison of commercial salts, volunteers given about 255 mg a day showed higher and equivalent urinary absorption from chloride, lactate and aspartate, and lower from oxide, which says nothing about skin.⁴ The chloride and sulphate rows of the forms directory are in types of magnesium, and the oral salts are compared in which magnesium is best.

Does magnesium spray help with sleep, cramps or sore muscles?

The trials the marketing leans on used magnesium by mouth. For sleep, the pooled evidence is three randomised trials in 151 older adults with insomnia: oral magnesium shortened time to fall asleep by 17.36 minutes against placebo (95% CI -27.27 to -7.44), total sleep time rose by 16.06 minutes without reaching significance, and the evidence was graded low to very low quality.⁵ No trial of a spray has a sleep outcome; see viral sleep rules and tricks for the foot-spray question and does magnesium help you sleep for the oral trials. For cramps, the 2020 Cochrane review found 11 trials in 735 people, all oral except one intravenous; in older adults the change in weekly cramps at four weeks was -9.59% against placebo (95% CI -23.14% to 3.97%), not significant, and the authors judged clinically meaningful benefit unlikely.⁶ NICE's clinical knowledge summary on leg cramps, revised December 2022, records that the review "concluded there was no benefit to magnesium supplementation", and the NHS leg cramps page, reviewed 1 December 2023, does not mention magnesium.^{8, 10} No trial has tested a spray or a bath for cramps or sore muscles. The authorised wording "Magnesium contributes to normal muscle function" belongs to the nutrient on a food's label, usable where a serving supplies at least 56 mg; a spray or a bath salt is not a food, so the wording is not available to it.^{11, 12}

Is magnesium spray safe, and who should avoid it?

Neither human study reported harm, and neither set out to record skin reactions.^{2, 3} Users commonly report tingling or stinging, most often on freshly shaved, dry or broken skin; no study has measured how often. Because no study has established how much magnesium reaches the blood from a spray or a bath, there is no systemic dose to count towards the NHS statement that 400 mg or less a day from supplements is "unlikely to cause any harm".⁷ Hangover patches that list magnesium raise the same delivery question, covered in hangover pills, patches and sachets. A bath for a child, or for anyone with eczema, psoriasis or an open wound, is a question for a pharmacist first.

If you want more magnesium, what has been shown to deliver it?

Food and supplements taken by mouth, measured in blood and urine across the oral trials above. The NHS puts the amount adults need at "300mg a day for men (19 to 64 years)" and "270mg a day for women (19 to 64 years)" and says 400 mg or less a day from supplements is "unlikely to cause any harm" (page reviewed 3 August 2020).⁷ What foods contain magnesium shows how far pumpkin seeds, nuts, wholegrains and pulses take you. On a supplement, read the elemental magnesium on the nutrition panel, not the compound weight. The oral salts are reported salt by salt, without a ranking, in how to choose a magnesium supplement.

What we don't know

Whether any spray, oil, flake or bath product delivers a measurable amount of magnesium to the blood: no controlled study has tested one at the dose it is sold at. How much, if anything, follicles and sweat glands let through in a real bath. Until a trial measures blood or urine magnesium after a commercial product against a placebo, the skin route has a mechanism argument against it and one small, non-significant pilot for it.

Frequently asked questions

Is magnesium oil the same as Epsom salt?

No. Magnesium oil and bath flakes are magnesium chloride; Epsom salt is magnesium sulphate. Both are about a tenth magnesium by weight and both are sold for the bath, not for swallowing.

How much magnesium is in an Epsom salt bath?

The salt is about 10% magnesium by weight, so a cup adds a known amount to the water. How much reaches your blood has never been measured in an indexed study, so there is no figure to give.¹

Can you use magnesium spray every day?

No study has measured daily use beyond four weeks, and none has found a systemic dose to limit.^{2, 3} Skin irritation is the practical limit: stop if it stings, keep it off broken skin, and ask a pharmacist before using it on a child.

Does magnesium spray work for restless legs?

No trial has tested a spray for restless legs, which is a different condition from cramp. For cramps by mouth, the Cochrane review found no meaningful benefit in older adults and NICE's summary says the same.^{6, 8} Restless legs that disturb sleep are a GP question.

Sources

1. Gröber U, Werner T, Vormann J, Kisters K. Myth or reality: transdermal magnesium? Nutrients, 2017. PubMed 28788060.
2. Kass L, Rosanoff A, Tanner A, et al. Effect of transdermal magnesium cream on serum and urinary magnesium levels in humans: a pilot study. PLoS One, 2017. PubMed 28403154.
3. Engen DJ, McAllister SJ, Whipple MO, et al. Effects of transdermal magnesium chloride on quality of life for patients with fibromyalgia: a feasibility study. Journal of Integrative Medicine, 2015. PubMed 26343101.
4. Firoz M, Graber M. Bioavailability of US commercial magnesium preparations. Magnesium Research, 2001. PubMed 11794633.
5. Mah J, Pitre T. Oral magnesium supplementation for insomnia in older adults: a systematic review and meta-analysis. BMC Complementary Medicine and Therapies, 2021. PubMed 33865376.
6. Garrison SR, Korownyk CS, Kolber MR, et al. Magnesium for skeletal muscle cramps. Cochrane Database of Systematic Reviews, 2020. PubMed 32956536.
7. NHS. Vitamins and minerals: others (magnesium). Page last reviewed 3 August 2020 (review overdue; re-read 12 October 2026). nhs.uk.
8. NICE Clinical Knowledge Summaries. Leg cramps: management. Last revised December 2022. cks.nice.org.uk.
9. British National Formulary. Magnesium sulfate. bnf.nice.org.uk.
10. NHS. Leg cramps. Page last reviewed 1 December 2023. nhs.uk.
11. Department of Health and Social Care. Great Britain nutrition and health claims (NHC) register. gov.uk.
12. Retained Regulation (EU) No 1169/2011, Annex XIII: nutrient reference values and significant amounts. legislation.gov.uk.

This article is general information, not medical advice.