Name: Magnesium stearate
Synonyms:Octadecanoic acid magnesium salt
Molecular Weight: 591.25
CAS Registry Number: 557-04-0
Magnesium stearate, also called octadecanoic acid, magnesium salt, is a white substance which is solid at room temperature. It has the chemical formula Mg(C18H35O2)2. It is a salt containing two equivalents of stearate (the anion of stearic acid) and one magnesium cation (Mg2+). Magnesium stearate melts at about 88 °C, is not soluble in water, and is generally considered safe for human consumption. Because it is widely regarded as harmless, it is often used as a diluent in the manufacture of medical tablets, capsules and powders. In this regard, the substance is also useful because it has lubricating properties, preventing ingredients from sticking to manufacturing equipment during the compression of chemical powders into solid tablets; magnesium stearate is the most commonly used lubricant for tablets. It is used to bind sugar in hard candies. It is also a common ingredient in baby formulas. In pure powder form, the substance can be a dust explosion hazard, although this issue is effectively insignificant beyond the manufacturing plants using it.
When used as a filling agent in the manufacture of capsules and tablets, such as vitamins, the source of this ingredient is typically bovine.] However, there is an increasing number of vegetarian options in which the product specifically indicates it contains magnesium stearate from vegetable sources.
Magnesium stearate is a major component of "bathtub rings". When produced by soap and hard water, magnesium stearate and calcium stearate both form a white solid insoluble in water, and are collectively known as "soap scum".