Melanoma in the nail bed: signs and next steps

A nail melanoma may appear as a brown or black vertical band under one nail. The band can become wider, develop uneven shades, or have irregular edges. Pigment may extend from the nail onto the cuticle or surrounding skin. The nail can crack, lift, bleed, or develop a persistent nodule. Melanoma can also be colourless, making a changing lump or damaged nail important to check.

Injury, infection, medication effects, and harmless pigment can look similar. A clinician considers the number of affected nails, whether the mark grows out with the nail, and changes in the surrounding skin. Examination and, when needed, a biopsy provide the basis for diagnosis.

Book a dermatology or medical assessment for a new streak, a band that changes, pigment crossing onto the cuticle, or a nail change that does not grow out. Remove nail polish before the appointment and bring older photographs if available. Avoid repeatedly filing, cutting, or treating the area for a presumed fungal infection without advice. If melanoma is confirmed, treatment may involve surgical removal and an assessment of nearby lymph nodes. See Melanoma, Surgical Excision, and Skin Cancer Surgery for related information.

Arrange prompt assessment when one nail develops a widening or irregular dark band, the pigment reaches the surrounding skin, or the nail begins to split or lift without a clear injury. Seek urgent help for uncontrolled bleeding, rapidly growing swelling, or severe pain with signs of infection. These signs guide urgency; they do not by themselves prove that the lesion is melanoma.

Ask whether the change could be trauma, infection, or another nail disorder; whether dermoscopy or biopsy is needed; and what the biopsy would show. If melanoma is diagnosed, ask about excisional surgery, sentinel lymph node biopsy, staging, follow-up after cancer treatment, and when systemic treatment might be discussed.