Quick Answer: Yellow-brown discolouration beneath the nail with a horizontal dark band, following trauma, that grows out with the nail is most suggestive of a post-traumatic nail bleed (subungual hematoma) — not cancer. The reassuring features: a trauma history, smooth localized pigmentation, no extension onto the surrounding nail fold, and steady outward movement as the nail grows. Subungual melanoma — a serious skin cancer under the nail — looks different, and any doubtful case warrants dermoscopy or nail biopsy. Traumatic nail bleeds need only observation and follow-up.
Case Snapshot: A worried patient asked: "Could this be toenail cancer? I had trauma to my left big toe, and it's been growing out for a while — you can see the line is moving upwards, but the dark area is still there. I am concerned." The images showed yellow-brown discolouration under the nail with a horizontal dark band — and the very feature causing anxiety (the moving line) was actually the most reassuring sign present.
The Two Diagnoses on the Table
Subungual hematoma is bleeding trapped under the nail plate after minor trauma — tight footwear, stubbing the toe, sports activity — producing brown, black, or reddish discolouration. Because the blood sits in or under the nail plate rather than in living tissue, it is carried passively outward as the nail grows, like a stain on a conveyor belt.
Subungual melanoma is a serious form of skin cancer that can occasionally arise under the nail — rarer, but the reason every dark nail streak deserves a considered look rather than automatic dismissal.
Why This Case Reads as Trauma, Not Cancer
The features favouring a benign post-traumatic bleed here:
- A clear history of trauma to that toe
- Smooth, localized pigmentation rather than an irregular expanding streak
- No extension onto the surrounding nail fold — pigment spilling onto the skin around the nail (Hutchinson's sign) is a melanoma warning, and it is absent
- The band is moving upward/outward with nail growth — dead blood rides the growing nail out; melanoma arises from the nail matrix and its band stays anchored at the base, persisting or widening rather than migrating away
The patient's worry — "the line is moving upwards but the dark area is still there" — describes exactly what a resolving hematoma does: the pigmented zone travels distally over months while fresh nail emerges clean behind it.
The Features That Would Change the Assessment
Dermatologists escalate when a nail streak shows: no trauma history; a longitudinal band starting at the cuticle and persisting or widening over months; irregular colour or blurred edges; pigment on the nail fold skin; involvement of a single digit in an older adult; or nail plate destruction, bleeding, or a non-healing area. Any of these earns dermoscopy and, where doubt remains, a nail biopsy — the definitive answer.
The Management Here
In traumatic nail pigmentation, treatment is usually conservative — observation and follow-up. Practically: photograph the nail monthly against a ruler or coin; expect the band to march outward and clear fully as the nail replaces itself (great toenails take roughly 9–12 months to grow out completely); protect the toe with roomier footwear so fresh trauma doesn't repaint the picture; and return promptly if the pigment stops moving, darkens at the base, or spreads to the fold. If there is any doubt, dermatologists may perform dermoscopy or sometimes advise a nail biopsy to confirm the diagnosis — a small price for certainty in a high-stakes differential. Our dermoscopy and biopsy services handle exactly these evaluations.
When to See a Dermatologist
See a dermatologist for any under-nail darkening without a trauma story, any band anchored at the cuticle, pigment on surrounding skin, a single-nail streak appearing in adulthood, or simply for the peace of mind of a dermoscopic check — nail melanoma caught early is highly treatable, and the examination is quick. Book a nail assessment.
FAQs
Q: How long until the dark area grows out completely? Fingernails renew in about 6 months, great toenails in 9–12. A hematoma clears on that schedule; anything persisting beyond it at the base deserves review.
Q: Should the blood be drained? Fresh, painful hematomas (within the first day or two) can be decompressed in clinic for pain relief. Old, painless discolouration like this case needs no drainage — only observation.
Q: Can tight shoes alone cause this without a memorable injury? Yes — repetitive micro-trauma from footwear or running commonly causes nail bleeds the patient never registers as an "injury."
Q: Is a dark vertical stripe in multiple nails dangerous? Uniform stripes across several nails are usually benign ethnic pigmentation, common in darker skin. The concerning pattern is a new, changing band in a single nail — still worth one professional look.
📌 Case Study Reference: Publicly shared patient images and query, r/DermatologyQuestions, Reddit — "Could this be toe nail cancer? I had trauma to my…". Educational discussion only; not a final diagnosis. Clinical commentary by the Allodermis dermatology team.
