I was thinking something like breath or air but since you can be lived without and are not inside a person I guess both of those are wrong. Then I thought skin cells, but since you are not skin that is too similar.
I really want to know the answer to Krakyn's guess before going too far, but here are a couple:
12) Are you bigger than a peach pit?
13) Are you soft to the touch?
Something that is organic in nature, active, not alive, touches your skin, and some are better without, not soft to the touch, and is replaced often.
13) are you used by man?
14) are you used by woman?
15) do you change the skin when you touch it?