A 53-year-old female asked:
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what causes black vertical lines under fingernails ? i am asking for a 66 yr. old male.

1 doctor answer
Dr. Laurence Badgley
53 years experience General Practice
Blood clots : Tiny blood clots, usually broken off from heart valves then float to the end arteries of the fingertips and get caught in the capillaries of the nail bed. They are not dangerous in and of themselves, but could be reflective of a heart problem.
Answered on Nov 26, 2020

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More info needed: Sounds like you damaged the nail bed at some point in time. Could also be fungal. Can you re-ask your question and attach a picture????
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