why do parents care so much about their kids drawing on themselves?

thankfully my parents never really cared and even went as far as buying me markers for skin, but i've had multiple friends who's parents would get mad at them for doodling on the back of their hand.

why?

they hardly give reasons other than "ink poisoning", but thats pretty difficult to get unless its on an open wound. it's usually just "dont do it".

it's such a trivial thing, why is it such a common concern among parents?