What should you know about longitudinal melanonychia?

The colour comes from increased pigment in the nail-making unit. It can affect one nail or several, and shades may range from light brown to very dark brown. Causes include normal pigment variation, repeated injury, inflammation, some medicines, and benign growths. A new or changing band on one nail deserves attention because, less commonly, pigment can arise from melanoma in the nail unit. A band itself does not establish cancer.

A dermatologist will inspect the band, the surrounding skin, and the nail surface with magnification. The width, colour pattern, borders, and whether pigment extends onto the nearby skin help guide the next step.

Photograph the nail in good light and record when you first noticed the band. Avoid picking, biting, or covering it with polish before an assessment. Mention recent nail trauma, manicure procedures, new medicines, and bands on other nails. A clinician may monitor a stable-looking band with planned photographs or may recommend a nail-unit biopsy when the appearance is concerning. Nail surgery can be used to obtain tissue, but the appropriate approach depends on the band and its location.

Arrange a dermatology review promptly for a new band on one nail, especially if it is widening, becoming darker or uneven, developing several colours, or reaching the cuticle or side folds. Seek earlier care if the nail splits, lifts, bleeds, or develops a persistent sore. These signs do not diagnose melanoma; they indicate that direct examination should not be delayed.

Ask whether the band has features that support observation, how often it should be photographed, and whether a biopsy is appropriate. Ask what nail changes should trigger an earlier visit and how to protect the nail while its cause is being clarified.