The following is an article about the safety of magnesium stearate. The short version is that magnesium stearate is used in manufacturing to keep the supplements from sticking to the machinery. The articles used to cast suspicion on the safety of magnesium stearate are grossly misquoted from what the studies actually say. You can generally assume that the tiny amounts of magnesium stearate in supplements is probably not contributing to your health problems. You may have a reaction to magnesium stearate but it is not a common issue.
Magnesium Safety Article