Causes and Risk Factors of Longitudinal Black Armor

Longitudinal black nail disease is the most common type of black nail disease, a medical term used to describe the black or brown pigmentation of the nail plate (the hard part of the toenail or nail).

Longitudinal black nails may look like partial or full stripes that run lengthwise (longitudinal) along the nail.

It can have many causes, from harmless pigmentation or growths to infections, systemic diseases or cancer.

This article will discuss the many causes of longitudinal black nail disease, what happens in nail cells, and how to diagnose it.

Overview of Common Nail Problems

Types of Longitudinal Black Nail Disease

Nail, hair, and skin color is determined by melanocytes Produces a pigment called melanin.

Cases of longitudinal black nail disease can be divided according to how they occur:

  • Melanocyte activation: Melanocytes produce additional melanin.
  • Melanocytic hyperplasia: The abnormal reproduction of melanocytes.

Melanocyte hyperplasia is especially concerning, given that melanocytes are prone to genetic errors as they reproduce. This can lead to benign (non-cancerous) or cancerous skin growths called tumors.


Longitudinal melanosis can be caused by an overproduction of a pigment called melanin or an overgrowth of pigment cells called melanocytes.

Common causes and risk factors

Many common causes of longitudinal melanosis are due to extra production of melanin.

Although the melanin in the nail plate is usually evenly distributed, it can sometimes become irregular.

With longitudinal black nails, the pigment cells at the base of the nail transfer melanin to the nail cells.

As the nail grows out, the melanin will be carried, forming longitudinal streaks from the nail fold or cuticle. This happens for a number of reasons, some of which are completely harmless.

Longitudinal melanosis, caused by excess melanin, is most common in people of African descent. It can also occur with nail trauma, systemic disease, or nail infection.

The cause of black nail disease can usually be diagnosed by a dermatologist, a doctor who specializes in treating the skin, hair, and nails.

nail trauma

Nail trauma, especially starting at or near the base of the nail, and Subungual hematoma, or blood under the nail, is a common cause of longitudinal black nails.

For example, if you hit your nail with a hammer, it will not only cause severe bruising from the accumulation of blood, but it will also “open” the melanocytes in the nail bed.

When this happens, melanin collects in the nail cells, causing a black or gray discoloration. This process is a form of melanocyte activation.

It’s no different that freckles darken when ultraviolet (UV) rays from the sun activate the melanocytes in the skin.


Fungal, viral, or bacterial infections can also cause streaks. These include:

  • subungual warts, warts under the nail plate, caused by viruses
  • Onychomycosisa common fungal infection of the nails
  • Chronic paronychia, a bacterial or fungal infection that occurs on the side of the nail where it comes in contact with the skin

Autoimmunity and Skin Conditions

Conditions affecting the skin and nails can cause longitudinal black nails. Autoimmune diseases, in which the immune system attacks the body’s own tissues, can also.

These conditions include:

  • Nail psoriasis, an autoimmune disease that causes nail changes
  • Addison’s disease, a type of adrenal insufficiency caused by an autoimmune disease, cancer, infection, or a pituitary tumor (growth of the pituitary gland)
  • Lichen planusAn inflammatory skin disease that may be caused by an autoimmune reaction


Longitudinal melanosis, caused by excess melanin, may result from nail damage, infection, and autoimmune disease. It usually occurs in people of African descent.

benign growth

When nail cells multiply abnormally, it is usually noncancerous.

Common types of benign growths that can cause longitudinal black nails include:

  • pyogenic granulomawhich are blood-red skin growths that sometimes occur during pregnancy or as a side effect of certain medications
  • Subungual exostoses, bony overgrowths on the fingertips or toes, which may be caused by persistent bone irritation
  • myxoid cysts, or small benign lumps that develop near the nail

How to tell if the cause is benign

Noncancerous longitudinal black nails often have the appearance of light to dark brown stripes that are parallel and regular in color, thickness, and spacing.

Boundaries will be well-defined and less than 3 millimeters (mm) wide, or approximately 1/10 of an inch.

Longitudinal black nail disease is extremely rare in children. When it does happen, 77.5% will be the result of benign growth.

Another sign that longitudinal melanoma is benign is a yellowish discoloration along the outer edges of the stripes. Black nail disease, which is caused by a serious illness, usually doesn’t go away.

Also, if the black mark is caused by an injury, it will tend to move toward the tip as it grows, leaving a flawless nail.


Streaks caused by noncancerous growths tend to have regular color, thickness, and spacing, with well-defined borders and widths less than 3 mm. However, it is important to have it checked by a healthcare provider.

Causes of loose toenails or nails

genetic cause

Longitudinal melanocytosis can occur with several rare genetic disorders in which hyperpigmentation of the skin (hyperpigmentation) is a common symptom.

Genetic diseases are caused by genes inside cells.

Many of these conditions are autosomal dominant, which means you only need to inherit the gene mutation from one parent to develop the disease.

Examples of genetic causes include:

  • Familial amyloidosis, a rare and potentially life-threatening disorder that occurs when a protein called amyloid builds up in organs and tissues
  • Laugier-Hunziker syndromea rare disorder with hyperpigmentation of the mouth, lips, fingers, and nails and a high risk of cancer
  • Peutz-Jeghers syndromea rare disorder that causes benign polyps in the gastrointestinal tract and hyperpigmented lesions of the mouth, lips, nails, and fingers
  • Turin syndromea rare, non-progressive disorder characterized by thinning body hair, brittle teeth, decreased ability to sweat, and hyperpigmented lesions


Sometimes, the tumor or growth that causes longitudinal melanoma is cancerous or potentially cancerous. This can include:

  • Subungual melanoma, a dangerous skin cancer that develops under the nail plate
  • Glomerular tumor, a rare and potentially fatal tumor found mostly under the nails, fingertips, or ends of the toes

Keratoacanthoma– Low-grade, dome-shaped tumors usually found on sun-exposed skin – can also cause longitudinal black nails. The cause of keratoacanthoma is unknown, but it is generally thought to be a squamous cell carcinoma, a type of skin cancer.

Lateral black nail disease is a rare form of black nail disease in which a dark line runs side by side along the nail plate. It is often associated with certain drugs and radiation therapy used to treat cancer.

Caring for your nails during chemotherapy

subungual melanoma

Melanoma accounts for about 1 percent of skin cancers, but is also the most dangerous.

Subungual melanoma, also known as nail stromal melanoma, is a type that primarily affects people over the age of 50 and is considered rare, accounting for only 0.7% to 3.5% of all melanoma skin cancers.

During a physical examination of the nails, doctors look for certain signs of cancer:

  • More than two-thirds of the nail plate is affected
  • grey or black mixed with brown
  • Irregular brown and granular pigmentation
  • Variation in stripe color and thickness
  • Blurred borders larger than 3mm
  • Deformation of the nail plate
  • Recurrent spontaneous bleeding from the same site

Subungual melanoma usually involves a single finger or toe, not multiple. Other symptoms may include longitudinal stripes on the affected fingers and darkening of the palms or soles of the feet.

Hutchinson’s sign is one of the main indications of subungual melanoma. This is when the streak runs from the tip of the nail all the way to the nail bed and into the cuticle.

Subungual melanoma can only be diagnosed by a nail biopsy. If there are suspicious signs, your healthcare provider may take a small sample of the nail for evaluation in a laboratory.

Early diagnosis and treatment can lead to better outcomes if problems are detected.


Rare genetic disorders and rare but serious skin cancers can cause longitudinal black nails. A fingernail sample is required to diagnose cancer.

environmental reasons

Longitudinal black nails also occur when pigments other than melanin enter the nail folds.

These can be taken up by the cuticle and underlying nail cells and carried along as the nail plate grows.

Examples include:

  • ink
  • Tar deposits from smoking
  • Hair dye or henna ink
  • Silver nitrate is used to treat burns and wounds
  • Potassium permanganate, which is a disinfectant sometimes used on the skin

If the cause is environmental, the streak usually doesn’t cross the crescent, the white crescent at the base of the nail. Discoloration may also appear on the edges of the skin below and around the nailfold.

Examination of the stratum corneum and review of the medical history can help healthcare providers identify environmental causes.


Other types of pigments from dyes, inks, or wound treatments can also cause streaks on the nails.

Common Salon Nail Infections


Longitudinal melanosis can be caused by overproduction of melanin (skin pigment) or an increase in melanocytes (pigment cells).

These increases in melanin, or melanocytes, can have a variety of causes, from harmless growths to injury, infection, or cancer.

VigorTip words

Black streaks on the nail bed can be distressing, but it doesn’t necessarily mean you have a disease or are at risk for it.

At the same time, it’s not something you should ignore, especially if the condition is persistent, affects most of the nail, or is associated with bleeding.

Have a healthcare provider look at it. Early diagnosis can make a big difference if it is due to a serious condition.