Magnesium stearate is the stuff that coats your medications and vitamins. You will commonly find magnesium stearate in foods, pharmaceuticals, and cosmetics. It acts like a lubricant which prevents capsules from sticking together.
Magnesium stearate is just a simple salt made up of a saturated fat called stearic acid and mineral magnesium. Stearic acid is naturally found foods like chicken, eggs, cheese, chocolate, walnuts, salmon, cottonseed oil, palm oil and coconut oil.
Magnesium stearate is thought to be safe to consume but, of course, if you have too much it could cause diarrhoea. There is some chatter on the internet about it causing all sorts of things while also having the ability to suppress your immune system but there is currently no evidence to back this up.