Black Streaks in the Finger Nails and Toe Nails

  • Streaks in the fingernails or the toenails can be very dangerous! I don’t want to scare you but it is entirely possible that a thick long dark streak could be melanoma- a type of skin cancer.
  • The odds of the streak in your fingernail are actually pretty low because a lot of people, especially African Americans normally have light thin streaks of dark pigment that that form a vertical line down their nail which is completely normal.
  • It is very easy to predict whether the streak is of the dangerous variety or if you are more on the safe side. It is essential that you see your podiatrist as soon as possible for a quick and easy biopsy if there is any doubt in your mind at all!


Dangerous causes of black streaks in the fingernail and toenail:

  • Subungual melanoma is the most dangerous cause. It is a very rare form of skin cancer; it is usually seen between ages forty to seventy. It is not due to sun exposure or trauma. It just appears one day without any incident. If your dark spot appears after an injury then you are most likely on the safe side.


Safe causes of black streaks in the fingernail and toenail:

  • Normal vertical streaks of pigment that are not melanoma. This is especially common in non-white individuals. These are usually thin lines in a very normal looking nail; check the guide below to see if you are on the safe side or if you should go get it checked out.
  • Trauma and loss of fingernail leading to a streak of blood. But this should eventually grow out at 1mm per month. If the blood is not advancing then you should get it checked out just to be safe!


Black Streaks in the Fingernails and Toenails

How to tell if you are safe:


Probably safe (but should still visit the podiatrist) if:

  • The streak is less than 3 millimeters in width.
  • The streak is uniform in length and of continuous color as it progresses down the nail.
  • The streak or pigment is only present in the nail and not in the skin.
  • The nail is not deformed, bloody or cracked in that area.
  • The nail looks normal compared to the other nails.



Visit a podiatrist for a biopsy immediately if:

  • The black streak is over 3 millimeters in width.
  • The streak is widest at the start of the nail origin.
  • The streak is not uniform or appears disrupted.
  • The streak changes color the further you get.
  • The streak continues from under the nail into the skin, termed “Hutchinson’s sign”.
  • The nail becomes deformed, bloody or starts to crack in the area of the streak.
  • The nail looks very unusual compared to the other nails.
  • The streak is more common in the thumb and the big toe.
  • The streak may even be white; in this case be aware of a nodule or irregularity that is forming under the nail plate.
  • If you have ever considered that there may be a wart underneath your nail that is just not healing.


Melanoma induced streak under the fingernail outlook and treatment:

The outlook is usually very good if the cancer is present inside the digit. Most people that suffer from this disease have avoided seeking treatment for many, many years and it has already spread to other areas of the body. If you are cautious and follow up on the streaking and ulcerating in a reasonable amount of time, you will most likely be safe. The cure consists of excising the lesion or amputation the tip of your fingernail. See your podiatrist as soon as possible!