What are dark lines in my finger nails?

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.