Why Nails Get Black Lines?

If there are black lines under your nails, you should not ignore this change, especially if your nails are bleeding and painful. The most common reason for black lines down a person’s nail is due to a condition known as melanonychia, which is brown/black pigmentation of the nail. This condition causes the nail bed to become darker. The less common reasons for nails getting black lines are: taking certain medications, HIV, scleroderma, Laugier-Hunziker syndrome, and Peutz-Jeghers syndrome.