Melanonychia is brown or black pigmentation of the nail unit. It commonly presents as a pigmented band arranged lengthwise along the nail unit, and this presentation is known as longitudinal melanonychia or LM.

The commonest cause of this band change is benign, increased production of melanin (black pigment) by the cells that produce it called melanocytes.

This is common in darker-pigmented individuals. Most affected individuals have more than 1 nail affected.

Rarely, it can be a sign of sub-ungual melanoma. The features to look out for that might suggest possible malignancy are:

• New onset
• 1 nail affected only
• Widening of the band at the edge of the nail ( not even )
• More than one colour
• Distortion of the nail plate
• If you are concerned you must see your GP who will undoubtedly refer you to Dermatology.