Melanonychia, also known as a dark or black line on the nail, causes a streak of dark pigmentation that runs along the nail ...

Not all marks on your nails are cause for alarm. "A black line that extends longitudinally from the cuticle to the free edge of the nail is often pigment," board-certified dermatologist Joshua ...

A black line in the nail may be simply a color variation, but it can also result from an injury. Other possible causes include the use of certain drugs and various health conditions, including HIV and ...