Magnesium oil (also referred to as transdermal magnesium) is a mixture of Magnesium chloride in water. In reality it is not an oil. It is applied to the skin. The magnesium is absorbed through the skin and is claimed to have health benefits, such as for the treatment of magnesium deficiency, to relieve muscle pains and aches (especially headaches), and enhance to relaxation.
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Magnesium oil Wikipedia(Text) CC BY-SA