Answer:
I build up castles. I tear down mountains. I make some men blind, but I help others to see. What am I?
If I drink I die. If I eat I am fine. What am I?
A dragons tooth in a mortals hand I kill I maim I divide the land.
I go inside boots and outside shoes. What am I?
I am the key that is the hardest to turn
What do you purposefully put lots of in and on your body, but run away from when you encounter it outside?