What are dark lines in my finger nails?

Pigment: Thisispigment from a mole qt base of nail. If there're multiple this is family charcteristic. However if there is only one it coukd rarely be a sign of a melanoma under the nail. That diagnosis requires a biopsy.

Not sure: Black stipes down one nail could be a subungual hematoma. Red or brown streaks could be splinter hemorrhages. Subungual Melanoma can cause nail ridges and dark colors of the cuticle. It usually begin in the nail matrix. It most often effects the thumbs or big toes. Get checked out when in doubt.

DARK LINES NAILS: In light-skinned people, dark lines can be due to medications, or depending how long it has been there, and on how many nails are involved, could be a rather serious tumor called melanoma. If you are dark-skinned, it could be a normal process, probably inherited. Your best bet is to see a dermatologist if this is new & something that has been worrying you.

Differing causes: Black stripes down 1 nail may be subungual hematoma. Red or brown streaks may be splinter hemorrhages. Brown/black lines from nail plate to tip are often seen in people with dark skin & are normal. Subungual Melanoma can cause nail ridges & dark colors of cuticle. It most often effects the thumbs or big toes. Dark lines may be due to other illnesses. Get checked out when in doubt.