A black line on the nail could be normal, such as when it is just a color variation. Other possible causes range from injury to certain medications for conditions like human immunodeficiency virus ...

Everyone is aware of the iconic school bus yellow, but have you ever stopped to think about the black lines on the side of the bus? Here's what they do.

A black line on your nail (medically known as melanonychia) causes a streak of dark pigmentation that runs along the nail bed. It can be a normal color variation, especially in people with darker ...