Medichoice Epsom Salts serves as a body muscle relaxant when bath salts dissolved in a warm bath. It can also be used a fabric softener or as a fertiliser. Epsom salt is also known as magnesium sulfate. Its well known as an ingredient used in a soak to treat minor aches and pains. It's thought to soothe tired muscles and reduce swelling. The most popular use for Epsom salt is in baths.