Epsom salt is a hydrated magnesium sulfate compound, with the chemical formula MgSO₄·7H₂O. It is composed of magnesium, sulfur, and oxygen atoms, and contains seven molecules of water (heptahydrate) for every molecule of magnesium sulfate. Epsom salt is a white, crystalline solid that is highly soluble in water. It is commonly used as a bath salt and in soaking solutions to relieve muscle pain and tension.