Magnesium stearate is a salt formed by a magnesium ion and two stearate molecules. Magnesium and alkaline earth metal and stearate is the anion of stearic acid, which is commonly present as a saturated fat in natural foods.
Studies have linked magnesium stearate to the weakening of the immune system, but some scientists have dismissed this claim. Stearate often derives from cottonseed oil, which has the potential to be contaminated with pesticides or genetically modified organisms. Some researchers have claimed products such as this are linked to health and environmental issues. In rare cases, humans can exhibit an allergic reaction to magnesium stearate.