I have a small white mark (1mm) on the tip of my thumb finger over the past 4 years and I went to hospital for the consultation with a dermatologist.after see this Dr put my finger on small tourch like equipment and take the image on the computer and then he told me to go the out side of his room and wait( in his room 4-5 medical students are also present)( it makes me worry)after 5 minutes he recall me and told that nothing to worry..it's not vitiligo...then what are the other possible reason for that permenent white mark