Melanonychia

Melanonychia is a darkened area — usually brown or black — in your nail. This can form in one or many of your fingernails or toenails.

A deposit of melanin in your nail plate causes melanonychia. Melanin is a substance within your body that gives your hair, eyes and skin their color. Your nail plate is made of keratin, which doesn’t have color.

Cells that contain melanin exist in your nails, but the cells aren’t active. Certain situations and conditions can activate these cells. A line or band of brown or black pigment then forms in your nail.

Melanonychia is a common condition that’s often harmless (benign). But it may be a sign of an underlying medical condition like melanoma, a type of cancer.

Types of this condition

The three types of melanonychia include:

• Longitudinal: There’s an up and down (vertical) darkened line on your nail plate. This is the most common type.
• Transverse: There’s a side-to-side (horizontal) darkened band across your nail plate.
• Total (diffuse): Your entire nail plate is dark.

Symptoms of melanonychia

The main symptom of melanonychia is an area of dark coloration in a fingernail or toenail. The area may:

• Be brown, gray or black
• Be a vertical line
• Be a horizontal line
• Cover your entire nail

Most commonly, it’s a vertical band. This streak can look like paint or residue from a marker. But it doesn’t wash off. It can form in any area of your nail.

If you notice changes to your skin or nails, see a healthcare provider. Melanonychia may be a sign of cancer or an underlying condition. So, it’s important to get an accurate diagnosis quickly.

Melanonychia causes

Melanonychia has several possible causes. The most common causes, which are all noncancerous, include:

• Bruised nail
• Mole (nevus) in your nail
• Repeated nail trauma, like nail biting, picking or friction from tight shoes
• Lentigos (“age spots” or “liver spots”) in your nail
• Genetics and race — people with medium to dark skin tones (more melanin) often develop it

Other causes include:

• Cancerous tumors, like subungual melanoma
• Connective tissue diseases, like scleroderma and lupus
• Fungal and bacterial infections
• HIV
• Hormone conditions, like Addison’s disease, Cushing’s syndrome and overactive thyroid
• Inflammatory skin conditions, like psoriasis, lichen planus and amyloidosis
• Medical procedures, like phototherapy and X-ray exposure
• Medications, like chemotherapy, ART and antimalarials
• Nutritional deficiencies, like vitamin B12 deficiency
• Pregnancy
• Warts

Risk factors

Melanonychia is most common in people with medium to dark skin tones. For instance, among people of Caribbean descent, it’s common to have nail discoloration by age 50. Nearly 20% of people of Japanese descent have benign melanonychia.

Complications of this condition

Complications depend on the cause of melanonychia.

Causes like trauma, infection and inflammatory conditions can damage your nails. They may split and be painful.

Subungual melanoma can lead to cancer spreading (metastasis). In general, melanoma in your nail has a poorer outlook than melanoma on your skin.

How doctors diagnose this condition

A healthcare provider will diagnose melanonychia after a physical exam. During this exam, your provider will learn more about you, your symptoms and your medical history. They’ll ask questions based on the ABCDEF method:

• Age
• Band identification, including the width and borders of the brown to black pigment of your nail
• Changes to the size and shape of the line in your nail and the amount of time it took for it to appear
• Digits (fingers/toes) involved
• Extension of pigment to surrounding skin
• Family history of melanoma or atypical moles

Your provider may suggest tests to see whether the change to your nail is noncancerous or cancerous. Tests could include:

• Looking at a clipping of your nail under a microscope
• Using a handheld microscope to view your nail
• A biopsy to study a small sample of your nail and skin under a microscope
• Imaging tests to look below your skin for any signs of cancer

How is it treated?

Treatment for melanonychia depends on the cause. If you have a benign form of it, you may not need any treatment — the discoloration is harmless and only cosmetic.

If the cause is an underlying condition, you’ll need to treat the condition. For example, you may need medications for an infection. Or you’ll need cancer therapies if you have subungual melanoma.

Your healthcare provider will be your guide. They’ll let you know whether you need treatment and what it entails.

What can I expect if I have this condition?

In most cases, melanonychia isn’t serious. If you have it because of your race or ethnicity, you’ll likely have it forever. If an underlying noncancerous condition is the cause, it may fade after a few months of treatment.

If cancer is the cause, the prognosis is usually poor. An early diagnosis and treatment of skin cancer leads to a better outcome. It’s very important to see a provider when you first notice changes to your skin or nails.