This in turn causes a type of anaemia known as megaloblastic anaemia, in which the red blood cells produced in the bone marrow are large and fragile.
These red blood cells are too large to pass out of the bone marrow and into the circulation.
Therefore, a person does not have as many red blood cells circulating around the body, and the skin will appear pale in colour.
The fragility of these cells also means that many of them break down, causing an excess of bilirubin.
Bilirubin is a slightly red or brown-coloured substance which is produced by the liver when it breaks down the old blood cells.
Large amounts of bilirubin are what gives the skin and eyes a yellow tinge.