Melanoma Under Nails: The Hidden Skin Cancer
Subungual melanoma is melanoma that develops under the nail plate - on a fingernail or toenail. It accounts for about 1-3% of melanomas in light-skinned populations but up to 15-35% in darker-skinned individuals, making it the most common melanoma subtype in Black, Asian, and Hispanic patients. It is often diagnosed late because people assume a dark nail streak is just a bruise.
What nail melanoma looks like
The hallmark sign is a longitudinal brown or black streak running from the cuticle to the tip of the nail (longitudinal melanonychia). Not all dark nail streaks are melanoma - most are benign, especially in people with darker skin. But certain features raise concern.
Worrying signs: the streak is wider than 3mm, the color is very dark or has multiple shades, the streak is widening over time, the pigment extends beyond the nail onto the surrounding skin (Hutchinson sign), or the nail is splitting or distorted.
The Hutchinson sign
When brown or black pigment extends from under the nail onto the surrounding cuticle or nail fold, this is called the Hutchinson sign. It strongly suggests melanoma and requires urgent biopsy. The pigment may be subtle - look carefully at the skin immediately surrounding the nail.
Who is at risk
Nail melanoma is the most common type of melanoma in Black, Asian, and Hispanic individuals. It also affects people of all skin types. The thumb and big toe are the most frequently affected digits. Unlike cutaneous melanoma, subungual melanoma is not strongly linked to UV exposure - its causes are not well understood.
Melanoma vs nail bruise vs fungus
A nail bruise (subungual hematoma) from injury is the most common mimic. Unlike melanoma, a bruise grows out with the nail over weeks to months and has a homogeneous color. Nail fungus (onychomycosis) typically causes yellowing, thickening, and crumbling - not a dark streak.
If you have a dark streak under your nail with no history of injury, or if a streak that appeared after injury does not grow out within 2-3 months, see a dermatologist.
Diagnosis and treatment
Diagnosis requires a nail matrix biopsy - a small sample from the root of the nail where the pigment originates. The nail may need to be partially or fully removed for proper biopsy access.
Treatment for nail melanoma follows the same staging and treatment principles as cutaneous melanoma: wide excision (which may mean amputation of the fingertip in advanced cases), sentinel lymph node biopsy, and systemic therapy for advanced disease.
Bob Marley and nail melanoma awareness
Bob Marley's death from melanoma that originated under his toenail has raised public awareness of this condition. He initially noticed a dark spot under his toenail which was diagnosed as acral lentiginous melanoma. The case highlights the importance of not ignoring persistent dark spots under nails, regardless of skin color.
Worried about a dark nail streak? Our ABCDE checker helps assess risk - but for nails, always see a dermatologist directly.
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