Magnesium hydroxide (chemical formula: Mg(OH)2) is a magnesium hydroxide that is white crystal or powder, insoluble in water, and widely used as a flame retardant, antacid, and stomach acid neutralizer. The suspension of magnesium hydroxide in water is called magnesium hydroxide emulsion, or milk of magnesium for short, and is used to neutralize excess stomach acid and treat constipation.