For many people, grey hair is a fact of life. It’s 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 your skin, hair and eyes their distinctive colours.
Melanin comes in two forms, eumelanin (black or brown) and pheomelanin (reddish-yellow). Combinations of these two create the spectrum of eye, hair and skin colours found among humans.
One way to understand how melanocytes determine hair colour is to think of these cells as tiny printers, applying their ink to paper. The paper in this case is our hair strands, formed of keratin, the same protein that makes up our fingernails.
Just as a printer sprays ink onto a sheet of paper to produce an image, melanocytes produce pigments that are embedded into the growing hair strand, providing them with colour. The melanocytes live within the hair follicle, so each hair strand has its own colour-producing printer.
While some people’s melanocytes print a lighter ink combination, such as blonde or red, others have darker colour palletes and so have black or brown colourations.
Now that we understand how hair gets its colour, we can understand why it goes grey.
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. However, age, exposure to chemicals and even the climate can influence how early the melanocytes die.
The strongest influence, however, is written in our genes. The genetic influence on hair colour is so strong that if your parents have grey hair, yours is likely to grey at around the same time as theirs did.
Jake Port contributes to the Cosmos explainer series.
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