What do dark vertical streaks on fingernails indicate?
Ask the doctor
Q. I have dark vertical lines on some of my fingernails. Overall, I'm healthy. What causes this condition?
A. Your description suggests a condition called melanonychia. It features brown or black streaks of the nail. It occurs because of increased pigmentation. But moles in the nail can also appear as dark streaks.
Melanonychia is more common in older people and darker-skinned people. It can also be seen after radiation therapy, after ultraviolet light exposure, while taking certain medications, during pregnancy, and with certain medical conditions. Melanonychia is uncommon in children.
It is very important to have a dark streak in a nail examined by a doctor because melanoma, a dangerous form of skin cancer, can also appear as a dark nail streak. This type of melanoma is called subungual melanoma. It will sometimes show a dark pigmentation on the skin at the edge of the streaked nail. This is called Hutchinson's sign and can be helpful in diagnosis. In some cases, your doctor may want to do a biopsy.
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About the Author
Howard E. LeWine, MD, Chief Medical Editor, Harvard Health Publishing; Editorial Advisory Board Member, Harvard Health Publishing
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