Having a dark line on your fingernails or toenails is called melanonychia. The lines are brown or black and usually look like a stripe that begins at the bottom of your nail bed and continues to the top.
Melanonychia can affect one or multiple nails and often appears as dark, vertical lines. It may occur naturally, especially in people with darker skin tones.
While many cases are harmless, it’s important to have any new or changing nail discoloration evaluated by a doctor, as it can sometimes signal an underlying condition.
Melanonychia is also known as melanonychia striata or longitudinal melanonychia.
There are two broad types of melanonychia:
- Melanocytic activation: This is an increase in the production and deposits of melanin in your nail, but not an increase in pigment cells. Causes include trauma, nutritional deficiency, and medication.
- Melanocytic hyperplasia: This is an increase in pigment cells (melanocytes) in the nail matrix, which is located under the base of the nail near the cuticle. This process is typically benign; however, similar pigment changes may also be seen in malignant conditions such as melanoma, so a doctor may need to examine it to distinguish between the two.
Melanonychia can appear in fingernails or toenails. It can also occur in more than one nail.
It may look like:
- a black or brown vertical stripe down the length of the nail
- a black or brown discoloration stripe spread across the nail
- a structural irregularity of the nail
The nails of your toes or fingers are usually translucent and nonpigmented. Melanonychia occurs when the pigment cells, called melanocytes, deposit melanin — brown-colored pigment — into the nail.
These deposits are usually grouped together. As your nail grows, a stripe of brown or black appears.
Causes of melanocytic activation can include:
- pregnancy
- racial variations
- trauma
- carpal tunnel syndrome
- nail-biting
- irregularity in your foot that causes friction with your shoes
- nail infection
- lichen planus
- psoriasis
- amyloidosis
- viral warts
- skin cancer
- Addison’s disease
- Cushing’s syndrome
- hyperthyroidism
- growth hormone dysfunction
- photosensitivity
- too much iron
- lupus
- HIV
- phototherapy
- X-ray exposure
- antimalaria drugs
- chemotherapy drugs
Causes of melanocytic hyperplasia can include:
- lesions (usually benign)
- moles or birthmarks (usually benign)
- cancer of the nail
Other causes of melanonychia may include:
- some bacteria
- tobacco
- hair dye
- silver nitrate
- henna
People of African descent are the
A diagnosis of melanonychia is reached after a series of exams. A healthcare professional may also review your medical history for conditions that might cause melanonychia.
They will likely examine your fingernails and toenails. This includes looking at:
- whether your nail has a structural irregularity
- how many nails have melanonychia
- the color, shape, and size of your melanonychia
A doctor may perform a dermatoscopic exam using a specialized microscope to closely examine the discolored areas. They typically look for signs that your melanonychia may be malignant.
The signs of possible nail melanoma include:
- discoloration that is more than
3 millimeters wide or has increased in size - irregular brown pigmentation
- black or gray color with the brown
- granular-looking pigmentation
- structural irregularity of the nail
The doctor may also perform a nail biopsy. However, because this procedure is somewhat complex and can have complications, melanonychia is often monitored over time.
A nail biopsy is usually recommended only if there are concerning signs that suggest possible cancer.
The treatment for melanonychia depends on the cause. If your melanonychia is noncancerous, you often do not need treatment.
If your melanonychia is caused by medication, a doctor may change your medication or have you stop taking it for a time, if possible. For medications that you cannot stop, melanonychia may be a side effect that you will get used to.
Other treatment options depend on the cause and may include:
- taking antibiotic or antifungal medications if infection is the cause
- treating the disease or medical condition causing the melanonychia
If your melanonychia is malignant (cancerous), the tumor or the affected area must be removed. That may mean you’ll lose all or part of your nail. In some rare cases, the finger or toe that has the tumor
Possible complications of melanonychia include:
- nail cancer
- bleeding under the nail
- splitting of your nail
- structural irregularity of your nail
The nail biopsy can also cause a structural irregularity by removing a portion of the nail.
What does a dark line on your nail mean?
A dark line on your nail can result from nail injury, certain medications, or medical conditions, or may be completely normal based on your ethnicity. A doctor can perform exams to determine whether melanonychia is malignant.
What causes dark stripes on nails?
Dark nail stripes typically appear due to increased melanin deposits, which give skin its color. Melanonychia can develop due to many causes, including nail cancer, trauma, and other health conditions.
What deficiency causes black lines on nails?
Deficiencies in vitamin B12, vitamin D, and protein can cause dark lines in nails. Other causes can include cancer, too much iron, and other health conditions.
What does stage 1 nail melanoma look like?
A dark vertical line on the nail can indicate nail melanoma. It can also occur with other benign causes and requires diagnosis by a healthcare professional.
Melanonychia is usually benign and does not require treatment, though it often does not resolve on its own. In rare cases, it can be malignant (nail melanoma), which is more serious and requires surgical removal of the tumor, sometimes including part of the affected finger or toe.
Because malignant melanonychia can closely resemble benign forms, especially in early stages, it can be difficult to detect, making a biopsy the most reliable method for accurate and early diagnosis.