Epsom salt, a magnesium sulfate compound, is a popular home remedy most commonly used as a foot soak. Taken orally or rectally as an enema, it is also used as a treatment for constipation. While some of the magnesium from these salts can be absorbed from the gastrointestinal tract, there is a lack of peer-reviewed research that supports a significant or therapeutic level of magnesium absorption from the skin. If you plan to use Epsom salt for the treatment of constipation, discuss the use with your doctor and follow package directions.
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Absorption Through the Skin
Epsom salt foot or body soaks are widely used as a way to relax muscles and relieve muscle tension. Since magnesium plays an essential role in muscle contraction and nerve function, it has been proposed that skin absorption of magnesium is the mechanism for these benefits. Despite these claims, there is a lack of peer-reviewed, published research supporting that topical application of magnesium increases body magnesium levels, according to a July 2012 review published in “International Journal of Cosmetic Science.” However, skin absorption could occur in the right conditions -- with heat, high salt concentrations or through cut or broken skin -- based on a review article published in the June 2014 issue of “Experimental Biology and Medicine.” Additional research is needed to better understand if soaking in Epsom salt leads to any meaningful magnesium absorption through the skin, as well as the health effects of any noted absorption.
Absorption Through the Gastrointestinal Tract
Since large amounts of magnesium have a laxative effect, drinking water with a small amount of Epsom salt is a common oral treatment for constipation. Epsom salt is also sometimes used as an enema. Either route will cause some of this magnesium to be absorbed. The small intestine is the primary site of absorption, although some is absorbed through the large intestine. According to a February 2012 report in “Clinical Kidney Journal,” the amount of magnesium that gets absorbed from the gut is highly variable -- as little as one-third may be absorbed -- and absorption is dependent on factors such as body magnesium level and source, including type type of magnesium compound.
Problems With Excess Absorption
Absorbing too much magnesium from Epsom salt poses health risks. While it's not likely Epsom baths or foot soaks will lead to significant magnesium absorption, using Epsom salt internally can pose risks of toxicity. For example, 1 tablespoon of Morton Epsom salt -- a typical amount used in the treatment of constipation -- provides approximately 1500 mg of magnesium, or about 4 times the Recommended Dietary Allowance. This is well above 350 mg -- the adult Tolerable Upper Intake Level (UL) for magnesium supplements set by the Food and Nutrition Board at the Institute of Medicine of the National Academies. The UL is the maximum daily intake that is unlikely to cause adverse health effects -- which for magnesium supplements can be diarrhea, nausea and abdominal cramping. Large doses can lead to more severe symptoms of magnesium toxicity such as decreased energy level, muscle weakness, difficulty breathing, very low blood pressure, irregular heartbeat and even death.
Warnings and Precautions
While an Epsom salt bath is generally considered a safe way to relieve muscle tension, relax muscles and soften skin, check with your doctor before using this product to treat any medical conditions or if you plan to use while pregnant. Excessive amounts of absorbed magnesium can lead to serious health effects, including death. If you plan to use Epsom salt to treat constipation, first discuss the use of this product with your doctor. If you have constipation that is accompanied by stomach pain, nausea, vomiting, fever or blood in the stool, do not self-treat and see your doctor.
Reviewed by: Kay Peck, MPH, RD