Skin & hair

A Brown Line on a Toenail — When It Needs Checking

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One dark band on a nail is one of dermatology's genuine look-alikes: a benign pigment streak and an early nail melanoma can start out identically. Here are the features clinicians actually weigh — width, how many nails are involved, color, whether pigment reaches the skin — and how quickly a new or changing streak should be seen.

Last updated: July 2026

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What a brown line on a toenail is

A brown line running the length of a toenail is a band of pigment laid down as the nail grows, a pattern doctors call longitudinal melanonychia. It appears when pigment-producing cells in the nail's root are switched on — by friction, a past injury, certain medications, or simply inherited pigmentation that is more common in darker skin. The same band can also mark a melanoma forming in the nail unit, known as subungual melanoma, because melanoma is a cancer of those same pigment cells 1. The stripe itself can look similar either way, which is exactly why a single glance rarely settles it.

The pigment is deposited into the hard nail plate at the base and then carried outward as the nail lengthens. So a streak is a record of what the root was doing weeks or months ago — useful context when a clinician tries to work out whether something changed.

When a nail streak needs a closer look

Certain features move a nail streak from routine to worth examining: a single band that is wide or steadily widening, one that is very dark or made of several shades, a band that first appears in adulthood, or one that changes over weeks to months. Dermatologists borrow the melanoma letter E — evolving — because a streak that shifts in width, color, or shape is more concerning than one that has looked the same for years 2.

Two other findings raise the level of concern. One is a band on a single nail, especially a thumb or big toe, rather than matching stripes across several nails. The other is pigment spreading to the nail cuticle and the surrounding skin fold — a finding clinicians call the Hutchinson sign. None of these confirms cancer, and none can be graded from a photo alone. They are simply the reasons a clinician recommends a proper evaluation rather than reassurance.

Is it a bruise or something more?

A dark patch under a nail is often just a bruise — a subungual hematoma from stubbing the toe, a dropped object, or shoes that press. The most useful distinction is movement: a bruise is trapped blood that grows out with the nail and travels toward the tip over weeks, while pigment produced at the root keeps forming and stays anchored at the base. That contrast — nail bruise vs melanoma — helps you describe what you are seeing.

It is not, however, reliable enough to settle the question alone. Some bruises sit still for a while; some pigment streaks are faint. If you cannot clearly watch a dark spot march toward the free edge of the nail over a month or two, that uncertainty is itself a reason to have it looked at.

What to photograph and track before your visit

While waiting for an appointment, the single most useful thing is documentation. A clear photo in good, even light against a plain background, with a coin or ruler beside the nail for scale, and the date noted, gives a clinician something a memory cannot. Measuring the band's width in millimeters helps too.

Repeating the same photo every few weeks turns a static image into a record of change. A before-and-after that shows whether the streak is widening, darkening, or spreading toward the cuticle answers the one question a single in-office glance often cannot. The appearance of a nail streak on any given day cannot confirm or rule out melanoma — how it changes over time, plus an exam, is what does.

How a nail streak is evaluated

A clinician usually starts by examining the nail closely, often with a dermoscope, and asking how long the band has been present and whether it has changed. When the picture is worrying, the definitive step is a biopsy of the nail matrix — the tissue at the root where the pigment is made. Guidelines call for a biopsy that samples the full thickness of the lesion, because if it turns out to be melanoma, its depth is what determines staging and the width of any later removal 3.

A matrix biopsy sounds daunting, but it is a short in-office procedure done under local anesthetic. It remains the only way to distinguish a benign pigment band from an early melanoma with certainty — no scan, phone app, or description substitutes for the tissue diagnosis 1.

Why timing matters

Melanoma found while it is still confined to the skin is highly treatable, and survival falls as it spreads to lymph nodes and beyond. Five-year relative survival is around 99% for melanoma caught while it is still localized, and drops below 40% once it has spread to distant sites 4. For a thin, early melanoma the treatment is usually surgical removal of the lesion with a margin of healthy tissue 1.

That gap is the whole reason a persistent or changing nail streak is worth a visit rather than a year of watchful waiting. Learning what happens after a melanoma diagnosis — the workup, the margins, the follow-up schedule — is a separate step that only becomes relevant once a biopsy has actually been read. The earlier decision, to get the streak examined, is the one that shapes those numbers.

Screening versus checking a specific streak

There is a real difference between routine screening and evaluating a streak that worries you. The US Preventive Services Task Force concluded that current evidence is insufficient to recommend for or against whole-body skin exams in adults who have no symptoms 5. That finding is about screening healthy, unconcerned people — it does not apply to a new, changing, or single-nail band, which is a specific reason to be seen.

People with a personal or family history of melanoma, many atypical moles, or heavy past sun exposure are the ones most often advised about who should get regular skin checks. For those readers especially, a new nail streak is worth a call sooner rather than later — not because a photo has diagnosed anything, but because the checking is what a diagnosis, if there is one, depends on.

Common questions

No. A brown nail band has several harmless causes, including friction, an old injury, certain medications, and inherited pigmentation. The difficulty is that a benign streak and an early nail melanoma can look alike at the start. Because appearance alone cannot confirm which one it is, an in-person evaluation is the safe way to sort it out.

A new single-nail band that appears in adulthood, or an existing one that is widening or darkening, is worth a dermatology visit in the coming weeks. It is not usually an emergency, but it is also not something to watch for a year. Documenting it with dated photos while you wait for the appointment helps the clinician judge whether it is changing.

Sometimes. A bruise under the nail tends to grow out toward the tip and disappears over weeks as the nail lengthens, while pigment made at the root stays anchored at the base. That difference can be a useful clue, but the overlap is real. If a dark spot is not clearly moving out with the nail, that alone is a reason to have it examined.

Matching bands across several nails are more often from generalized pigmentation than a band isolated to one nail, but multiple streaks do not rule anything out on their own. Clinicians still weigh width, color, change over time, and whether pigment reaches the surrounding skin. The pattern is one piece of information, not a verdict you can reach without an exam.

The Hutchinson sign is pigment that extends from the nail onto the adjacent skin — the cuticle or the fold around the nail. Clinicians treat it as a feature that raises concern for a nail melanoma and prompts closer evaluation, often a biopsy. Like every single feature, it is one input a clinician weighs, not something that confirms or excludes cancer by itself.

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When a nail change is worth prompt attention

  • —A single dark band on one nail that is widening or getting darker over weeks to months
  • —Brown or black pigment spreading from the nail onto the surrounding cuticle or skin fold (the Hutchinson sign)
  • —A new pigmented band appearing on one nail in adulthood, especially a thumb or big toe
  • —A nail streak with associated nail splitting, a nodule, or bleeding at the base

This article is educational and cannot diagnose your nail. No description, photo, or checklist replaces an in-person exam, and only a biopsy can tell a benign pigment band from a melanoma with certainty. If a nail change concerns you, arrange an evaluation with a clinician or dermatologist.

References

  1. 1.National Cancer Institute (PDQ Adult Treatment Editorial Board) (2025). Melanoma Treatment (PDQ®)–Health Professional Version. NIH / National Cancer Institute. link ✓Melanoma is a cancer of pigment-producing cells and can arise in the nail unit; tissue diagnosis is how melanoma is confirmed, and early, thin melanoma is treated by surgical excision with a margin.
  2. 2.Abbasi NR, Shaw HM, Rigel DS, et al. (2004). Early diagnosis of cutaneous melanoma: revisiting the ABCD criteria. JAMA. PMID 15585738 ✓The 'E — evolving' feature of the ABCDE criteria: a pigmented lesion that changes in size, shape, or color over time is a warning feature for melanoma.
  3. 3.Swetter SM, Tsao H, Bichakjian CK, et al. (2019). Guidelines of care for the management of primary cutaneous melanoma. Journal of the American Academy of Dermatology. doi:10.1016/j.jaad.2018.08.055For a suspected melanoma, biopsy should sample the full thickness of the lesion so that tumor depth can be measured for staging.
  4. 4.National Cancer Institute, Surveillance, Epidemiology, and End Results (SEER) Program (2025). Cancer Stat Facts: Melanoma of the Skin. NIH / National Cancer Institute (SEER). linkFive-year relative survival for melanoma of the skin is about 99% when localized and falls below 40% once it has spread to distant sites.
  5. 5.US Preventive Services Task Force (2023). Skin Cancer: Screening. US Preventive Services Task Force. link ✓The USPSTF found current evidence insufficient to assess the balance of benefits and harms of whole-body visual skin screening in asymptomatic adults; the finding addresses screening, not evaluation of a concerning lesion.

5 sources, numbered by first appearance. General health information, not medical advice. AI-assisted editorial content — citations link their sources. Editorial policy

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