Dark Lines on Nails in Black Skin: Normal Pigment or Melanoma?

Dark brown or black lines running from the base of the nail to the tip are called longitudinal melanonychia. In Black adults they are common and usually harmless: a review in the International Journal of Women's Dermatology reports this kind of band in almost 100% of Black patients by age 50, often on several nails at once (Ezenwa et al., 2021). Rarely, a single dark band is the first sign of nail melanoma, which in Black patients is often found late. The difference is in how the band looks and whether it changes, and that is what this guide teaches you to check.

The nail is made by a strip of tissue under the cuticle called the matrix. The matrix has pigment cells, and when they switch on, they lay a stripe of melanin into the growing nail that travels up to the tip. A 2025 clinical review by a group of nail experts in the Journal of the American Academy of Dermatology explains that most bands come from this kind of pigment activation, which can be physiologic, from injury or friction, from medicines, or from other conditions, while a smaller share come from a nail mole and a rare few from melanoma (Ricardo et al., 2025).

In people with darker skin, the pigment cells are more active to begin with, so these stripes are routine. The Women's Dermatology review describes ethnic melanonychia as common in skin of color and notes that involvement of several fingers is a sign that the bands are benign. The bands most often appear on the fingers you grip with (the thumb, index and middle fingers) and on the big toe, places that take the most pressure (Ezenwa et al.). A widely cited older figure puts the prevalence at 77% of African American adults, which a 2023 pediatric case series repeats (Andrade et al., 2023).

Normal pigment bands tend to share a few features:

• They are on more than one nail, often on both hands.
• They are light to medium brown or gray, with an even color along their length.
• Their edges are straight and parallel, and their width is the same at the base and the tip.
• They stay the same for years.
• The skin around the nail is your normal color.

The Women's Dermatology review adds a caution: even when someone has many benign bands, any band that looks markedly different from the others should be checked (Ezenwa et al.).

Dermatologists at Columbia published a nail version of the melanoma ABCDs in 2000, and it is still the most practical checklist (Levit et al., 2000):

• A, age. Nail melanoma peaks in the 5th to 7th decades of life. The authors also flag African American, Asian and Native American patients, in whom nail melanoma makes up as much as a third of all melanomas.
• B, band. Brown to black, 3 mm wide or more, with blurry or uneven borders.
• C, change. A band that is widening or darkening, or a nail that does not get better after treatment for something else, such as fungus.
• D, digit. Which nail is involved. The AAD says nail melanoma most often appears on the thumb or big toe of the dominant hand or foot, and the Women's Dermatology review notes that bands on several nails point toward a benign cause, so a single nail is the one to watch.
• E, extension. Pigment spreading onto the cuticle or the skin beside the nail, called Hutchinson sign.
• F, family. A personal or family history of melanoma or atypical moles.

The Women's Dermatology review lists more features that raise suspicion when a dermatologist looks with a dermatoscope: a band covering more than two-thirds of the nail's width, irregular lines with uneven spacing and width, gray or black lines on a brown background, and a band that is wider at the base than at the tip, a triangle shape that can mean the pigment is growing (Ezenwa et al.).

The American Academy of Dermatology also lists dark skin next to the nail, a nail that lifts from the nail bed, a nail that splits down the middle, and a bump or nodule under the nail. It says nail melanoma is more common in older people and in people with skin of color, and advises seeing a board-certified dermatologist for any new dark band (AAD, How to check your nails for melanoma).

Melanoma is less common in Black people, but when it happens it is more often diagnosed at a later stage, and acral types, the ones on palms, soles and nails, make up a larger share of cases, according to a 2023 continuing-education review in the Journal of the American Academy of Dermatology (Brunsgaard et al., 2023). The Women's Dermatology review notes that nail melanoma has a higher relative incidence and higher mortality in skin of color (Ezenwa et al.).

Part of the delay is that a dark nail band in a Black adult is so often normal that patients and clinicians both stop looking. Part is that nail melanoma is easy to mistake for something else. The same review notes that nail melanoma is misdiagnosed in about half of cases and that most patients do not recognize the nail changes associated with it (Ezenwa et al.). The AAD adds that nail melanoma is often diagnosed at a later stage than melanoma on the skin (AAD).

For the bigger picture on melanoma of the palms, soles and nails, including where to look on your feet, see our guide to acral melanoma on Black skin. For skin cancer of every type, see skin cancer on Black skin.

Not every dark stripe is melanin. The nail experts' review sorts the causes into pigment from outside the nail plate (dirt, dyes, tobacco), blood, bacteria and fungus, and pigment from the nail's own melanocytes (Ricardo et al.). Common examples:

• Blood under the nail. After an injury, often from shoes or a slammed finger. It looks red-purple to black, does not form a neat stripe, and grows out with the nail over weeks to months.
• Fungal infection. Some fungi stain the nail brown or black, usually with thickening, crumbling or yellowing as well.
• Medicines. Some prescription drugs can switch on nail pigment. If bands appeared after starting a new medicine, tell your doctor which one.
• Friction and injury. Repeated pressure or trauma to the nail, from tight shoes or picking at the cuticle, can trigger pigment.
• A nail mole. More common in children. It still needs to be followed by a dermatologist.

A dark band in a child is a different situation. A 2021 review in Pediatric Dermatology notes that almost all causes of dark nails in children are benign and that melanoma is extremely rare at that age (Bellet, 2021). The nail experts' review adds that benign bands in children can look worrying, even sharing features of adult melanoma, so they recommend a conservative approach with close follow-up rather than an automatic biopsy (Ricardo et al.). A pediatric dermatologist is the right person to set that schedule.

Once a month, in daylight, look at every fingernail and toenail, including under polish. Photograph any band straight on with a ruler beside it, and look at the skin around the nail. Compare with last month. A band you have photographed for a year without change is very different from a band that is new or growing, and the photos tell your dermatologist that in seconds.

At the appointment, a dermatologist will usually look at the band with a dermatoscope, a lighted magnifier. Sometimes they clip a piece of the nail for testing. If the band is suspicious, the definitive test is a biopsy of the nail matrix. The nail experts' review calls this the gold standard for ruling melanoma in or out, and describes nail clippings and dermatoscope exams as useful first steps that can avoid a biopsy or help plan one (Ricardo et al.). Because a matrix biopsy is a surgical procedure, dermatologists reserve it for bands with real warning signs.

Make an appointment with a board-certified dermatologist if you notice:

• A new dark band on one nail as an adult, especially on a thumb, index finger or big toe.
• A band that is getting wider, darker, or has more than one shade in it.
• A band wider at the base than at the tip, or 3 mm or wider.
• Dark pigment spreading onto the cuticle or the skin beside the nail.
• A nail that splits, lifts, bleeds, or has a bump under it, especially after an injury you cannot clearly remember.
• A dark mark under the nail that you took for a bruise but that does not move forward as the nail grows.

None of these needs an emergency room. They do need a dermatologist rather than a wait-and-see. To find one who sees skin of color regularly, search our provider directory.