A black line on the nail could be normal, such as when it is just a color variation.
They are typically due tomelanonychiaor splinter hemorrhages, both of which stem from multiple underlying factors.
Melanonychia
Melanonychia is characterized by black or brown discoloration of the nail plate.
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It’s relatively common, accounting for about half of allnail discolorationcases.
It can affect one or multiple nails on the fingers and toes.
If the discoloration is medication-related, it usually appears soon after starting treatment.
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Fungal infections:A fungal nail infection can cause longitudinal melanonychia.
While rare,Candida infection of the nailcan sometimes present with a black line, mimicking melanoma.
A fungal infection can be confirmed with a nail biopsy or culture.
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Black lines on the nail occur with endocarditis due to damaged blood vessels.
This results in a thin, dark line that runs vertically along the nail.
Common causes include hitting the nail, prolonged pressure, or habits like nail biting.
Psoriasis:Psoriasis, an autoimmune skin condition, can sometimes present with a splinter hemorrhage.
As many as 80% of people with psoriasis have it on their nails.
For example:
Your symptoms will also vary depending on whether you have melanonychia or a splinter hemorrhage.
If the change happens suddenly, seek medical attention right away.
Your provider may order diagnostic tests like a nailbiopsyandblood teststo confirm their suspicions.
Treatment
Melanonychia and splinter hemorrhages are usually not treated directly.
If a health condition is responsible, managing that condition is the priority.
Similarly, if medications cause it, you may notice other medication side effects.
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2021;13(4):e14248.
doi:10.7759/cureus.14248
American Academy of Dermatology Association.How to check your nails for melanoma.
2015;151(8):907-908. doi:10.1001/jamadermatol.2015.0388
National Library of Medicine.Splinter hemorrhages.
Canal-Garcia E, Bosch-Amate X, Belinchon I, Puig L.Nail psoriasis.Actas Dermosifiliogr.
2022;113(5):T481-T490.
