Strange Blue around the tip of fingernail.?

Question

I've had this for a while, at first i thought maybe i rubbed against a pen(somehow, while it seems impossible). I have this strange blue line all across the tip of my fingernail, it looks like a pen mark, i tried getting it to go away, it won't rub off and keeps coming back.
Anyone have any idea what this could possibly be?

Answer 1

A blue line rather than a blue hue is unlikely to be pulmonary insufficiency. Also schleroderma and Renaud's phenomena are not usually so restricted. See a dermatologist and set your mind to rest.

Answer 2

You're a blue blood.

Answer 3

arsenic poisoning