An abnormality of the fingernails in which they become thin, brittle, and spoon-shaped, with edges that turn upward. Koilonychia is a recognised clinical sign of iron-deficiency anaemia, though it can also occur in other conditions affecting nail growth. The nail changes develop gradually as prolonged iron shortage impairs the formation of healthy nail tissue. Doctors look for spoon nails during physical examination as a clue to underlying deficiency, confirming it with blood tests for ferritin and haemoglobin. Correcting the iron deficiency through diet or supplements usually allows normal nails to grow back over several months.