What should you know about traumatic melanonychia?

A knock, tight footwear, nail biting, picking, or repeated friction can disturb the nail unit and cause pigment or bleeding beneath the nail. The result may look brown, black, or reddish and can be tender at first. As the nail grows, a trauma-related mark may move toward the tip. The nail may also split, lift, or develop a temporary ridge.

Not every dark nail change is caused by trauma, even when an injury is remembered. A clinician considers the pattern, surrounding skin, number of nails involved, and whether the mark is progressing. Persistent discolouration may need examination, and rarely a nail procedure is discussed when the diagnosis remains uncertain.

Avoid the pressure or activity that caused the injury, keep the nail trimmed without cutting into tender skin, and do not pick or drill the discoloured area. Wear well-fitting shoes and protect the finger from further impact. Photograph the nail periodically in similar lighting and note pain, swelling, lifting, or movement of the mark. Remove polish before a clinical review so the nail and surrounding skin can be seen.

Seek assessment if pain is severe or worsening, the nail becomes increasingly swollen or warm, pus develops, the nail lifts extensively, or you cannot use the affected finger or toe normally. Arrange a dermatology review when the mark does not move with nail growth, changes without further injury, spreads onto surrounding skin, or has no convincing traumatic explanation.

Ask whether the pattern fits trauma, how long observation is reasonable, how to protect the nail, which changes need urgent review, and whether nail surgery or another test is warranted.