I just noticed this randomly and it only appears on my index, middle, and ring fingers. Could this be caused by typing? They are the fingers I use the most. I don't type "properly" because that slows me down lol.
You can see what I'm talking about here: http://i.imgur.com/bR30JXP.jpg
It's very faint in the image but there's 2-4 vertical lines on each of the fingers. I'm fairly certain this isn't any health issue, just a strange thing I've noticed and now am wondering what causes it.