Black line on nail: 10 Causes, Diagnosis, Treatment, When to see a Doctor

Black line on nail causes can range from simple discolouration to life-threatening cancer like Melanoma. So, we need to be aware of the causes, symptoms and diagnosis of the black line on fingernail. So that we can take prompt action when we see a dark line on nails, and get appropriate treatment without delay.

Black line on nail Causes:

black line on nail
Black line on nail
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There are many causes of developing a black line on nail. Let us explore all of them below:


Injury or trauma is one of the most common reasons for forming a black line on nail or dark lines on nail. You can get your nail injured due to accidents or motor vehicle accidents, something heavy like a hammer falling on your hand while working, etc.

When your nail on your finger is injured, the blood vessels beneath the nail will burst to result in leakage of blood and the appearance of blood beneath the nail like a black line on nail.

Sometimes, injury of your nail leading to the formation of the black line on fingernail can happen due to some minor reasons like someone squeezing your fingers with pressure while playing some game, etc.

Infective Endocarditis:

Infective endocarditis is the inflammation or swelling of the Endocardium of the heart due to some infections, either bacterial or fungal. Do you know what endocardium is? Three layers of tissue cover our heart. The outer layer is the pericardium, the middle layer is myocardium or muscle tissue, and the inner layer is called the endocardium.

Infective endocarditis can present with many symptoms in the affected person including the development of black line on nail. He may also suffer from other symptoms like joint pains, fatigue, swelling of limbs, pain in your chest, etc.

This condition is generally seen in people who have any other heart diseases priorly. Bleeding below the nails called splinter haemorrhages are seen in half of the patients with Infective Endocarditis. This gives the appearance of dark lines on nails.

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Psoriasis is a chronic skin ailment in which the growth cycle of the skin cells is altered. In this disease, there is the formation of red, scaly patches, plaques on the skin. These patches on the skin have silvery white scales most of the times.

In people affected by Psoriasis, splinter haemorrhages are present below the nail. Just like Infective endocarditis, half of the people affected by this condition have these haemorrhages below the nails, which look like a black line on nail.

Splinter haemorrhage:

Splinter haemorrhages are the long red lines or stripes that appear below the nail, giving the appearance of the black line on nail. Trauma can cause them, and also due to conditions like Infective endocarditis and Psoriasis.

Just now, we have discussed Psoriasis and Infective Endocarditis. Let us know other conditions, which also cause splinter haemorrhages under the nail. Some examples of such conditions are:

  • Inflammation or swelling of blood vessels due to various causes, a condition known as Vasculitis
  • Infections, like bacterial, viral or fungal infections
  • Connective tissue disorders like SLE or Systemic lupus erythematosus, Raynaud disorder
  • Diseases of the circulatory, respiratory or renal systems
  • Therapy or drugs given for cancer side effect
  • As a side effect of drugs affecting blood coagulation
Beau’s lines:

Beau’s lines appear like horizontal ridges or grooves or lines over the nail running from side to side of the nail. They might affect all the nails that we have at one time. They represent underlying disorders in the body. Some such conditions causing the formation of Beau’s lines are:

  • Metabolic disorders or disorders of metabolism like Diabetes mellitus or Thyroid problems
  • Sexually transmitted infections like Syphilis
  • Viral illnesses like Mumps

Melanoma is a type of skin cancer affecting the melanocytes of the skin and the nail. It is a life-threatening or fatal cancer. So, any black line on nail should be promptly evaluated without delay to rule out Melanoma skin cancer.

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The type of Melanoma affecting nails is called Subungal melanoma, where subungal means below the nail. Hutchinson sign helps us in differentiating the black line on nail caused by Melanoma from other causes of the black line on fingernail.

In Hutchinson sign, there is discolouration or black coloured pigments on the skin which is present adjacent to the nail which has a black line on nail. So, if you notice any discolouration of the skin beside the nail having a black line on nail, consult a Dermatologist without delay for fast diagnosis and treatment.


There are several medications which can cause black line on nail as a side effect, for example, drugs used for the treatment of Malaria, Cancer medication, Anti-Hypertensive drugs of a particular type like Beta- Blockers, etc.


There are many infections which can cause black line on nail. These include viral infections like Mumps, HIV, Bacterial infections like Syphilis and also Fungal infections. The fungal infection that causes black line on nail or sometimes white or yellowish discolouration of the nails is called onychomycosis.

Connective tissue disorders:

Several connective tissue disorders like Lupus or systemic lupus erythematosus, Raynaud’s syndrome, Scleroderma or Systemic sclerosis, etc. also cause the development of black line on nail or dark lines on nails.

Rare syndromes:

Some rare syndromes can also cause the development of this black line on fingernail. For example, Peutz Jegher syndrome. But, this syndrome is rare to occur. So, it is a rare cause of black line on nail.

Black line on nail Diagnosis:

The diagnosis of the black line on nail happens in several stages just like any other medical condition. At first, your physician will take a detailed history of your symptoms, their severity, duration, etc.

He might also ask about the medications you have been taking for any condition. Then he will perform a physical examination to check for rashes on your body, etc.

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He will also examine the exact appearance of your nails. He might perform further tests including blood tests, biopsy, etc. based on the findings of your history and physical examination. He can conclude the condition you are having after correlating findings from your history, physical examination and the investigations performed.

Black line on nail Treatment:

The treatment option for the black line on nail depends on the underlying cause of the problem. For some causes like trauma, there is no particular treatment required. It will resolve on its own. But, for conditions like Psoriasis, oral drugs and ointments to apply locally need to be used.

For Infections, the appropriate antimicrobial agent needs to be used depending on the cause of the infection, whether it is a bacteria, virus or fungus.

For a condition like Melanoma, which is a dangerous type of cancer, the affected nail and the skin beneath is removed to prevent further spread of cancerous cells. If the bone is affected by melanoma, the finger might require amputation as well.

When to see a Doctor for the Black line on nail:

You need to see your doctor straight away if you notice any discolouration of your nail or blackness of your nail without any history of trauma. This is because we need to rule out severe conditions like melanoma at first and know the cause of development of black line on nail.

If the cause of the dark lines on nails is benign as per your doctor’s diagnosis, then you can relax without much worry. But, you need to consult your doctor without delay to know the cause of black line on nail.

You have seen all the possible causes, diagnosis and treatment methods of black line on nail. So, whenever you notice any such symptoms, ensure to contact your physician and rule out any dangerous disorders.  This is because the majority of life-threatening disorders are treatable when diagnosed early. Better to be safe than to regret later.

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