From the photo, you seem to have a longitudinal band of pigmentation on the nail plate. This is termed medically as longitudinal melanonychia. You do not have a splinter haemorrhage which affects usually just part of the distal nail and not the entire length of the nail in a uniform manner.
The origin of the longitudinal melanonychia lies in the nail matrix which is located below the proximal part of the nail plate under the nail fold.
In adults, causes of longitudinal melanonychia include increased activity of normal pigment forming cells (melanocytic activation), an increased cluster of benign mole cells as well as subungual melanoma.
Clinically, it may be difficult to distinguish melanoma for non-melanoma especially in the early stages. Early consultation with a dermatologist is recommended and a nail matrix biopsy may be needed to exclude subungual melanoma.
