Small, sparse, numb spots on skin?

I have 3 small, numb spots on my skin. They are kind of indented and if I rub my finger over them, I can't feel a thing. I was messing with one on my arm and accidentally caused it to bleed because I just can't feel it. It started with on on my forearm, then noticed on around my shin, today a found a new on on my thigh. Does anyone have any idea of what these could be?