Answer:
Deep, deep, do they go. Spreading out as they go. Never needing any air. They are sometimes as fine as hair.
I am always around you but often forgotten. I am pure and clean most of the time, but occasionally rotten. What am I?
What dress does everyone have, but no one wears?
In many hall ways you would stand if not with me in hand.
Without a bridle or a saddle across a thing I ride a-straddle. And those I ride by help of me though almost blind are made to see.
What do you purposefully put lots of in and on your body, but run away from when you encounter it outside?