Supplement analysis backed by scientific evidence · PT

← All supplements
Limited evidenceSleep & relaxation

Magnesium Sulfate (Epsom Salt)

Magnesium sulfate works as an osmotic laxative when swallowed, which is well established. The popular claim that a warm Epsom bath delivers magnesium through the skin is not supported by the available permeation data.

Evidence last reviewed: August 2026

What the science says

  • Laxative effect when taken orally Moderate evidence

    A double-blind, placebo-controlled RCT of sulfate-rich mineral water in people with functional constipation found increased stool frequency and improved consistency. This osmotic mechanism is the long-standing pharmacological use of magnesium sulfate.

  • Absorption through the skin during a bath Limited evidence

    An ex vivo study of magnesium delivery through intact and barrier-disrupted human skin found negligible transport across an intact skin barrier. A small pilot RCT of transdermal magnesium cream likewise found no clear change in serum magnesium, so a relaxing soak is most plausibly warm water and rest rather than magnesium repletion.

  • Relaxation and muscle soreness Limited evidence

    There are no controlled trials showing that Epsom salt baths reduce muscle soreness, cramps or anxiety compared with a plain warm bath. Any benefit reported by users cannot be separated from the effect of heat and immersion themselves.

Dosage & safety

Studied doseAs an oral laxative, typical adult doses are 5–10 g dissolved in water, used occasionally and not as a daily habit. For baths there is no evidence-based dose; labels usually suggest 1–2 cups per tub, which is a comfort choice rather than a studied one.
SafetyOral magnesium sulfate causes cramping and diarrhoea and can lead to dehydration or dangerous hypermagnesaemia in people with kidney impairment — they should avoid it entirely. Do not use oral magnesium sulfate for undiagnosed abdominal pain or suspected bowel obstruction, and not repeatedly without medical advice. Baths are low risk apart from skin irritation, but avoid hot soaks in pregnancy or with cardiovascular disease.

Scientific references

Where to buy

View on iHerb

Referral link — this site may earn a commission on purchases.

Related in Sleep & relaxation