Melanonychia: Understanding a Dark Stripe on Your Nail

What Is Melanonychia?

Melanonychia refers to brown or black pigmentation (color) in the nail plate. The most common form is longitudinal melanonychia, where a dark stripe or band runs from the base of the nail to the tip, following the direction of nail growth.

The pigment visible in the nail plate comes from melanocytes — the pigment-producing cells found in the skin and also in the nail matrix (the tissue at the base of the nail that makes the nail). When melanocytes in the nail matrix become active and produce melanin, that pigment gets incorporated into the nail as it grows, creating a dark streak that travels along the length of the nail.

Longitudinal melanonychia is significantly more common in people with darker skin tones. Studies show it occurs in up to 77-96% of Black adults and up to 10-20% of Asian adults, where it is usually a normal finding. In Caucasian individuals, a new dark nail stripe is less common and warrants more careful evaluation.

What Causes a Dark Nail Stripe?

There are two main categories of causes:

Benign (Non-Cancerous) Causes — the majority

• Ethnic/racial melanonychia: normal increased melanocyte activity in people with darker skin tones; often affects multiple nails, stable over time
• Nail matrix nevus (mole): a benign cluster of melanocytes in the nail matrix producing a pigmented stripe; common in children and young adults
• Laugier-Hunziker syndrome: a benign condition causing pigmented stripes on multiple nails, sometimes with pigment on the lips and mouth
• Medications: many drugs cause nail pigmentation as a side effect, including antimalarials (hydroxychloroquine), certain chemotherapy agents, HIV antiretroviral drugs (zidovudine), tetracyclines, and amiodaron
• Trauma: repeated minor nail injury can stimulate melanocytes
• Inflammatory nail conditions: nail lichen planus, nail psoriasis
• Systemic diseases: Addison’s disease (adrenal insufficiency), pregnancy, HIV infection
• Nail infections: some fungi can produce pigment that resembles melanonychia

Concerning Cause — requires exclusion

• Subungual melanoma (nail melanoma): a rare but potentially life-threatening cancer arising from melanocytes in the nail matrix. This accounts for 0.7-3.5% of all melanomas overall, but represents a higher proportion of melanomas in people with darker skin (up to 20% of melanomas in Black Americans, and up to 30% in Asians). It most commonly affects the thumb, index finger, or big toe.

How Can You Tell If It Is Dangerous?

This is the critical question — and the reason any new dark nail stripe should be professionally evaluated. Dermatologists use clinical and dermoscopic examination to assess risk. Features that raise concern for melanoma include:

• Width: a band wider than 3 mm, or one that is getting wider over time
• Color: uneven color within the band (multiple shades of brown, black, gray), or a band that suddenly darkens
• Borders: blurry or irregular borders rather than sharp, parallel edges
• The Hutchinson sign: dark pigment spreading from the nail onto the surrounding skin (the nail fold or fingertip skin) — this is a significant warning sign
• Nail changes: nail splitting, thinning, or destruction associated with the stripe
• Single nail: a stripe on only one nail, especially in an adult over 50 with no clear benign explanation
• Change over time: a stripe that was stable and is now visibly changing in width, color, or characteristics

It is important to know that neither you nor your doctor can definitively distinguish a nail nevus from early nail melanoma by appearance alone — which is why biopsy is often recommended when uncertainty exists.

How Is Melanonychia Diagnosed?

Your dermatologist will examine the nail and surrounding skin, often using dermoscopy (a hand-held magnifying instrument that allows detailed examination of nail structures and pigment patterns). They will also ask about:

• When you first noticed the stripe
• Whether it has changed
• Your medications and medical history
• Family history of melanoma

Based on this assessment, they may recommend:

• Observation: monitoring with photographs every 3-6 months for low-risk stripes
• Biopsy: a small sample of the nail matrix tissue is taken to examine under a microscope. This is the only way to definitively rule out melanoma. Nail biopsy can be done under local anesthetic as an office procedure, though the nail may be temporarily altered.

Treatment

Treatment depends entirely on the underlying cause:

• Benign ethnic melanonychia or drug-induced: no treatment needed; drug-induced pigmentation often fades when the medication is stopped
• Nail matrix nevus: can be monitored if low-risk features are present, or excised if there is diagnostic uncertainty or concerning features
• Nail melanoma: requires surgical excision with appropriate margins; staging determines whether further treatment is needed. Early diagnosis dramatically improves outcomes.

When to See a Dermatologist Urgently

• A new dark stripe appearing on a nail, especially if you are fair-skinned or over age 50
• An existing stripe that changes in color, width, or pattern
• Dark pigment spreading from the nail onto the skin of the nail fold (Hutchinson sign)
• A dark nail stripe accompanied by nail destruction or deformity
• Any single-nail dark stripe with no obvious benign cause

Frequently Asked Questions

I am Black and have dark stripes on several nails — is this something to worry about?

Multiple dark stripes on several nails in a person of darker skin tone are very commonly benign — this is the most common presentation of racial melanonychia and is often a normal finding. That said, even in people with darker skin, a stripe that is new, suddenly widening, developing irregular color, or spreading onto the surrounding skin deserves professional evaluation. The baseline of “normal for me” makes it especially important to notice any changes.

My child has a dark stripe on a fingernail — how concerned should I be?

Dark nail stripes in children are most often caused by nail matrix nevi and are typically benign. Nail melanoma is exceedingly rare in children. However, all nail matrix nevi in children should be evaluated by a dermatologist and monitored, as some do grow or change and may require biopsy for reassurance. The approach is usually watchful waiting rather than immediate biopsy unless features are worrying.

What does a nail biopsy involve?

A nail matrix biopsy is a minor office procedure. After the toe or finger is numbed with local anesthetic, a small sample of the nail matrix (the tissue producing the pigment) is taken. The nail plate may need to be partially lifted to access the matrix. Some temporary nail deformity is expected but usually resolves as the nail regrows. The sample is examined by a pathologist. While it sounds daunting, for dark nail stripes with uncertain features it provides definitive information and peace of mind.

How is nail melanoma different from skin melanoma?

Nail melanoma (subungual melanoma) behaves similarly to other acral lentiginous melanomas — it tends to grow slowly and is often diagnosed late because nail changes are dismissed or overlooked. Because it is under a nail and difficult to see clearly, diagnosis is delayed on average 1-2 years from when the stripe first appeared. This is why early evaluation matters: melanoma caught before it invades deeply has an excellent prognosis. Delayed diagnosis after the nail plate or underlying bone is involved significantly worsens outcomes.

Trusted Resources

• American Academy of Dermatology — Nail Melanoma
• Skin Cancer Foundation — Melanoma
• Mayo Clinic — Melanoma

Always consult a board-certified dermatologist for diagnosis and personalized treatment recommendations. This information is for educational purposes only and does not replace professional medical advice.