Vertical lines on thumb Hello doctors, I noticed a parallel vertical light black lines on my left thumb about a month ago. It's still there as it is. It is NOT thick, but it is very They do not pain or have changed any colour. From a distance it just looks like ridges, but if I examine nearby, then I can see the lines. They are not there in any other fingers. What could this be? Vitamin deficiency? I consulted a primary physician and he told it was nothing.