Answer:
I am a protector. I sit on a bridge. One person can see right through me, while others wonder what I hide. What am I?
Whoever made me doesn't want me. Whoever bought me doesn't need me. Whoever uses me doesn't know me. What am I?
No matter how hard you hit me, no matter how much I hurt, I'll always go for a laugh. What am I?
What goes around the wood but never goes into the wood?
I have no voice but I can teach you all there is to know. I have spines and hinges but I am not a door. Once I’ve told you all I cannot tell you more.
What do you purposefully put lots of in and on your body, but run away from when you encounter it outside?