Grey hair is a sign that we are getting older and that our bodies are going through change. To understand why hair turns grey, we first need to understand why it has colour in the first place. The answer is a special type of cell known as a melanocyte. These produce melanin, the pigment that gives our skin, hair and eyes their distinctive colours. You can think of melanocytes as tiny printers: just as a printer sprays ink onto a sheet of paper to produce an image, melanocytes produce pigments that are embedded into the keratin that forms our growing hair strands, providing each hair with colour. In hair, grey is not a colouration like any other shade: it is the lack of colouring. The keratin of people with grey hair lacks pigment because their melanocytes have died, revealing the natural grey-white colour of the keratin protein. Because each hair strand has its own melanocytes, some go grey before others. Exactly what decides which strands go grey first is still unknown. The strongest influence, however, is written in our genes. The genetic influence on hair colour is so strong that the age at which people's hair goes grey is similar from generation to generation.