Nail Bruise or Melanoma — How the Two Behave

How a nail bruise usually behaves

A subungual hematoma is blood trapped under the nail plate, usually after a knock — a dropped object, a stubbed toe, a shoe that presses on a long run. It starts red or purple and darkens toward brown-black over the following days. The feature that gives it away is movement. As the nail grows, the mark drifts toward the fingertip and a clear, normal zone opens up behind it at the base.

On a fingernail the whole thing usually grows out over a few months; a toenail can take closer to a year, because toenails grow more slowly. If you remember the injury and the mark is inching forward week by week, that pattern fits a bruise. a bruise migrates out with the nail; a melanoma band stays anchored at the base. But 'fits a bruise' is not the same as 'is a bruise' — which is the whole reason to keep watching rather than to stop thinking about it.

How subungual melanoma tends to behave

Subungual melanoma usually appears as a brown-to-black stripe running the length of the nail, from the cuticle to the tip — a pattern called longitudinal melanonychia. Unlike a bruise, it does not march forward and clear. The pigment stays anchored at the base, and over months the band often widens, darkens, or grows uneven along its edges. A band that is changing this way — the E for evolving in the ABCDE melanoma warning signs — is the feature that most often prompts a biopsy 1Ref 1Abbasi NR, Shaw HM, Rigel DS, et al. (2004).Early diagnosis of cutaneous melanoma: revisiting the ABCD criteria.A changing or evolving lesion is the 'E' added to the ABCDE early-melanoma criteria, supporting change over time as a warning feature that prompts evaluation..

A few details raise the level of concern, though none of them makes a diagnosis on its own:

• One nail, not many. A single affected digit, most often a thumb or a big toe, is more worrying than faint, even bands on several nails at once.
• Width and edges. A band wider than a few millimetres, or one with blurred rather than crisp borders, draws attention.
• Spread onto the skin. Pigment creeping onto the cuticle or the nail fold is its own warning, covered in the next section.
• Nail damage. Splitting, a lump, or bleeding within the pigmented area.

This is where a dark streak under the fingernail that appeared with no injury behind it earns a second look rather than a shrug.

Pigment spreading to the cuticle: Hutchinson's sign

When the brown or black pigment extends beyond the nail onto the surrounding skin — the cuticle or the nail fold — that finding has a name: Hutchinson's sign. Dermatologists treat pigment spreading to the nail cuticle as a meaningful warning feature for subungual melanoma, enough that it is generally a reason to sample the nail rather than to keep watching it.

It is not proof of cancer on its own. Several harmless situations can mimic it, and the only way to sort the real finding from a look-alike is an in-person exam. But pigment on the skin around the nail moves the situation out of the 'watch and photograph' category and into the 'be seen soon' one.

The one test that actually settles it

There is no way to tell a stubborn bruise from an early melanoma with certainty by eye, by phone photo, or even by dermoscopy alone. The answer comes from a biopsy — a small sample of the nail matrix or the pigmented tissue, read under a microscope. For a suspected melanoma, clinicians favour a full-thickness sample rather than a superficial shave, because the depth of the tumour is what determines its stage and a partial sample can under-measure it 2Ref 2Swetter SM, Tsao H, Bichakjian CK, et al. (2019).Guidelines of care for the management of primary cutaneous melanoma.For a suspected melanoma, a full-thickness biopsy is preferred over a superficial shave because tumor depth drives staging; a partial sample can under-measure it..

If the sample is benign, that is the end of it. If it shows melanoma, the thickness and other features guide what comes next — usually a wider excision of the area, and sometimes a sentinel lymph node biopsy to check whether any cells have travelled to the nearest nodes 3Ref 3National Cancer Institute (PDQ Adult Treatment Editorial Board) (2025).Melanoma Treatment (PDQ®)–Health Professional Version.After diagnosis, melanoma treatment is guided by thickness/stage and may include wide local excision and sentinel lymph node biopsy.. Knowing the diagnosis is what makes the treatment the right size; guessing does not.

How fast should a nail change be seen?

A dark nail with a clear, remembered injury that is visibly growing out can reasonably be watched — a photograph every couple of weeks, in good even light, against the same plain background, so real change is obvious rather than remembered. A band that appeared with no injury behind it, sits on a single finger or toe, is widening, or shows pigment creeping onto the skin belongs in front of a clinician within weeks, not filed away for a year.

A teledermatology visit can be a fast first door. A clear, well-lit photo submitted through a store-and-forward service can help a dermatologist decide how urgently you need an in-person appointment and a biopsy 4Ref 4American Academy of Dermatology (2024).Teledermatology Standards.Store-and-forward teledermatology can triage a photographed lesion and route the patient to in-person evaluation and biopsy.. It is a triage tool, not a substitute for the biopsy itself: a photo cannot diagnose melanoma, and it should not be used to talk yourself out of an exam.

Why finding it early matters

Melanoma caught while it is still thin and confined to where it started is far more treatable than melanoma found after it has spread. across all melanomas of the skin, five-year relative survival is about 94%, and above 99% while the tumour is still localized 5Ref 5National Cancer Institute, Surveillance, Epidemiology, and End Results (SEER) Program (2025).Cancer Stat Facts: Melanoma of the Skin.US melanoma five-year relative survival is about 94% overall and higher than 99% for localized disease.. The distance between those two numbers is the reason a dark nail is worth the small trouble of a check.

Part of why nail and other acral melanomas are sometimes found late is precisely the assumption this page is about — that a dark nail must be a bruise. Most of the time it is. But the cost of checking a bruise is a quick visit, and the cost of dismissing a melanoma is measured in stage. That asymmetry is the whole argument for photographing it, tracking whether it moves, and having anything unexplained looked at.