ABSTRACT
The term ‘chromonychia’ indicates an abnormality in colour of the substance or the surface of the nail plate and/or subungual tissues. Generally, abnormalities of colour depend on the transparency of the nail, its attachments and the character of the underlying tissues. Pigment may accumulate due to overproduction (melanin) or storage (haemosiderin, copper, various drugs), or by surface deposition. The nails provide a historical record for up to 2 years (depending on the rate of linear nail growth) of profound temporary abnormalities of the control of skin pigment which otherwise might pass unnoticed. Colour is also affected by the state of the skin vessels, and by various intravascular factors such as anaemia and carbon monoxide poisoning.
