Striate melanonychia: what to know about a dark nail line

The band usually runs from the cuticle toward the nail tip and may be brown, grey, or black. It can affect one nail or several. Causes include normal pigment variation, repeated injury, inflammation, infection, medicines, and changes within the nail’s pigment-making cells. A band is not automatically cancer, but a new or changing band in one nail needs an in-person examination because appearance alone cannot reliably identify its cause.

Photograph the nail in good light, note when the band began, and avoid biting, picking, or covering it with polish before assessment. A clinician may examine the band with magnification and inspect the surrounding skin and other nails. If the cause remains uncertain, a small sample or Nail Surgery may be discussed. You can also read about Discoloured Nails while arranging an appointment.

Arrange a dermatology review promptly if the band is new, widening, irregular in colour, spreading onto the cuticle or nearby skin, or associated with nail splitting, lifting, bleeding, or a lump. Earlier assessment is also sensible when only one nail is affected and there is no clear injury. Sudden pain, pus, or marked swelling needs prompt care for possible infection or trauma.

Ask whether the band needs monitoring, what features make sampling useful, whether another nail or skin condition could explain it, and how to protect the nail while it grows out.