Answer:
I am long and slim works in light. Has but one eye and an awful bite.
Use me if you really want to see inside someone
I go in hard come out soft. Blow me hard and I’ll make a pop.
I cannot be bought cannot be sold even if I’m sometimes made of gold.
When I point up, it's bright. When I point down, it's dark. What am I?
What do you purposefully put lots of in and on your body, but run away from when you encounter it outside?