I need help to stop picking at nails and skin

So every once in a while I will just start just destroying my nails and the skin around it. I know alot of fourms are about biting nails, but i dont do that...

But I just pick and pick and pick. I think i do it cuz i look at my nails and go, well this is dirty and this is not straight and even and i just keep going, i even sometimes get a nail clipper and just clip and clip and clip until i basically have nothing. I even do this with my toes.

My friends tell me I even do this when i dont even realize I am. I just wanna stop. It is painful but I just cant seem to stop myself from doing this.