Photograph of the thumb of a person suffering from iron deficiency anaemia, showing the characteristic brittle, spoon-shaped nail, a condition known as koilonychia. Anaemia is a disorder of the blood in which the quantity of haemoglobin (the red, oxygen-carrying pigment) is reduced. It can have a number of causes, including a deficiency in the dietary iron required for haemoglobin synthesis. Symptoms include excessive tiredness, breathlessness, pallor and, more rarely, skin and nail abnormalities. Iron deficiency is extremely common, particularly in pregnant women and pre-school children.