What's the main difference between "mess up" and "screw up?"

Native speaker’s answer
Rebecca
"Screw up" is just more informal than "mess up." But there's no real difference between the two! You can use them interchangeably. Ex: I'm sorry, I screwed up. = I'm sorry, I messed up. Ex: She screwed up the performance so badly. = She messed up the performance so badly.