What should you know about transverse melanonychia?

A horizontal band runs across the width of the nail, unlike a lengthwise pigmented band. It may involve one nail or several and can appear as the nail grows. Causes include pressure or trauma, inflammation around the nail, illness, some medicines, or increased pigment activity. Colour alone cannot identify the cause. A clinician will consider the affected nails, the skin around them, the band’s pattern, and whether the mark is moving outward with nail growth.

A photograph and examination can help separate melanonychia from other forms of discoloured nails. In an unclear case, the clinician may discuss monitoring or a nail procedure to examine tissue.

Think back to recent knocks, repetitive pressure, manicures, picking, new medicines, or inflammation. Avoid biting, aggressive filing, and further trauma while you observe the nail. Take a clear photograph and note whether the band changes as the nail grows. Do not cover a persistent unexplained mark with polish before an examination, because the clinician may need to inspect the nail and surrounding skin.

Arrange a dermatology assessment for a new band with no clear trigger, a mark that changes, pain, nail splitting, bleeding, swelling, or pigment extending onto the surrounding skin. Seek prompt care if several nails change with feeling unwell or after starting a medicine. A clinician can decide whether observation or nail surgery is appropriate.

Ask whether the band is moving with nail growth, what causes fit its pattern, whether photographs are enough for monitoring, and what findings would make sampling or nail surgery useful.