I have a light black/brown thin line exact in the middle of the left hand thumb. There in no pain or etching. I don't remember any injury on the thumb. I consulted to a doctor, (not a Dermatologist) he informed me that it was due to fungal infection. I took medicine for a week. The line didn't vanish neither it become dark. Later I went to him and showed him, he informed that the line has become little bit light and nothing to worry and he informed me to ignore. Its not on any other finger on hands or Leg. Is this a serious issue? Do I need to take a second opinion especially from a Dermatologist? Does this need urgent attention?