Are Black Lines on Fingernails Melanoma?

Your fingernails can tell you a lot about your health. In this article, we’re going to talk about a symptom that affects quite a bit of people: black lines in fingernails.

Most people who see this symptom automatically think melanoma. While this is certainly a possibility, it’s not as likely as some other causes that we’re going to talk about.

In fact, most fingernail lines end up being benign and harmless. However, there’s no way to known for sure until you speak with your doctor.

If your doctor’s visit is several days away, and you’re looking for some peace of mind, then read this article to the end. It may help you feel less anxious about your scary symptom.

What Does a Single Black Line Mean?

Black Lines on Fingernails

Black lines on fingernails can mean a number of things. They are typically characterized by a single line or streak that runs down the length of the nail.

First off, know that 75% of cases of fingernail melanoma involve a thumb or big toe.

So if your line is on any other finger or toe, then your chances of having cancer go way down (these numbers were given by the British Journal of Dermatology).

What else should you look for? Keep an eye out for discoloration that’s increasing in width.

That’s a sign that cells are actively dividing, which could mean cancer. To know for sure, a doctor will need to go in and do a biopsy.

After a few days, they’ll be able to confirm whether or not it’s melanoma. Don’t worry- it most cases, it will be an injury or a harmless mole.

Bottom Line: In 75% of cases, fingernail melanoma occurs on a big toe or the thumb.

What Direction Are Your Black Lines in Fingernails Facing?

The direction by which the lines are facing can also tell you whether or not it’s dangerous.

Lines running horizontally are considered more dangerous than lines running vertically.

This isn’t a concrete rule, just a general guideline. As you can imagine, there may be cases in which the opposite is true.

However, this is a good rule of thumb to follow. If you notice that your line is horizontal and black in color, you may want to schedule a visit with your doctor.

Bottom Line: Lines that run horizontally are more likely to be malignant than lines running vertically, although it’s not a guarantee.

Fungal Infections

Believe it or not, it’s possible to develop a fungal infection underneath your nail. When this happens, it can mimic fingernail melanoma.

In the medical community, a fingernail fungal infection is called onychomycosis. While not particularly life-threatening, it can cause your nails to look abnormal.

It’s estimated that up to 1 in 10 adults in Western countries suffer from toenail fungal infections. If you’ve got black lines on fingernails, this could be the primary cause.

Bottom Line: Fungal infections of the nails are quite common. Yet, most people don’t even realize that they have one.

How to Treat a Fingernail Fungal Infection

Most fungal infections are superficial, or near the top of the fingernail. For this reason, they’re relatively easy to get rid of.

Most doctors will prescribe you a topical treatment that should relieve your symptoms.

If for whatever reason your symptom is still there afterwards, you may need to follow up with your doctor.

Remember that fungal infections are relatively common and won’t kill you. They’re often caused by poor hygiene, which you can fix from home.

Bottom Line: There are many ways to treat a fungal infection of the nail. These include natural and medical interventions.

Other Possible Causes

Splinters or foreign debris getting stuck underneath the fingernail can cause a black line to appear. You should be able to remember if something like this happened to you.

Sometimes, these lines are simply genetic and require no medical intervention.

Pencil lead is a debris that a lot of children get stuck under their nails when they’re in school.

If it’s a child with black lines in fingernails, then explore the possibility of it being caused by pencil lead.

Bottom Line: If something gets stuck underneath the nail (wood, piece of lead, etc.), it can cause a black line to appear.

When Should You Worry?

Be on the lookout for additional symptoms like fever, bruising, and bleeding as it could indicate a possible infection.

If you’ve got other strange symptoms that you can’t explain, along with your fingernail lines, then this might be a cause for concern and should be explored further.

If you have no additional symptoms, try not to stress as the underlying cause is probably benign.

Bottom Line: If you’re feeling anxious, schedule a visit with your doctor. They’ll be able to determine whether you have melanoma.

What is Melanoma?

Melanoma is one of the deadliest forms of cancer. The reason why? Because it gets detected too late.

The good news is that you have an extremely good chance of surviving melanoma if you catch it in the early stages, especially if you’re young and healthy.

Even older people have a good chance of survival as long as the melanoma hasn’t spread to other parts of the body.

Melanoma is caused when pigment cells begin to divide uncontrollably. Over time, they can travel to other parts of the body and eventually form a tumor. That’s when they become deadly.

Pay Attention to Your Fingernails

Most doctors would agree: fingernails can tell you a lot about your overall health.

If something doesn’t look right, including black lines on fingernails, then you need to explore further. It might be melanoma, but chances are it’s nothing serious.

You shouldn’t ever take any chances with your health. Be on the lookout for additional symptoms and see your doctor if you become too worried.

Related Questions

Light Brown Lines under Nail

Ask a Question: If you want to ask a medical doctor a question that hasn't been answered in one of our articles go to: Ask a Medical Doctor About your Symptoms

Did you find the information in this article helpful?


  • My boyfriend has lines in his nails the thumb, pointer finger and his middle finger. He thinks it’s nothing but I’m worrying and does it mean it’s something bad being in more then one finger?

  • My husband is having brownish vertical line on his light leg’s thumb. I am really bery worring about that.plz suggest something

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