A black line on your nail (medically known as melanonychia) causes a streak of dark pigmentation that runs along the nail bed ...

Fingernail ridges are visible lines or grooves on the nail’s surface. They can run vertically from the cuticle to the tip of the nail (known as longitudinal ridges) or horizontally across the ...

The skin and nails may deteriorate if the body lacks the necessary building blocks to create new cells. Black-brown vertical lines in the nail plate are known as longitudinal melanonychia ...