Fifty shades before grey

By Anna Tiley

A recent conversation with a friend somehow turned to the topic of human hair colour. What determines hair colour? And why does it change with age?

In order to answer this question, we first need to look at what exactly hair is. It’s commonly known that hair is made out of dead cells and a protein called keratin. But hair doesn’t start off dead. Living hair cells are actually made under the skin in pore-like structures called follicles. As these cells are made, they replace the older ones, pushing them up towards the surface of the skin. The older cells are filled with protein then lose their nucleus and die.

Surprisingly, hair cells aren’t coloured. In fact, hair is naturally white. The colour comes from the pigment melanin which is made by melanocyte cells at the base of the hair. These cells produce the melanin and inject it into the living hair cells, thus giving them colour.

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There are two types of melanin pigment, eumelanin and pheomelanin, and the ratio of these determines hair colour. Eumelanin makes hair black or brown whereas pheomelanin makes hair ginger or blonde. People with black or dark brown hair will have very high levels of eumelanin and low levels of pheomelanin. In contrast, people with blonde hair will have more pheomelanin than eumelanin. Red heads have the highest proportion of pheomelanin to eumelanin.

An interesting property of pheomelanin is that it breaks down more slowly than eumelanin. This is why bleaching brown hair often results in an orangey colour. The bleach doesn’t react as readily with the pheomelanin so it has to be left in longer in order to obtain the perfect ombre shade!

The reason why hair goes grey and white with age is a different matter. It is believed that this happens due to a natural depletion of melanocytes. Without the melanocytes, no melanin is made or deposited into the hair cells and the hair is no longer coloured.

Genetic disorders in hair colour, on the other hand, are due to mutations in the genes responsible for melanin production. As a result, melanin isn’t made or deposited into the hair cells.

Understanding the process of hair pigmentation can help in the development of methods to restore hair colour. One such study looked at the possibility of transplanting melanocytes from hair follicles into Yucatan mini pigs. This could potentially be a way of restoring hair colour in people with pigmentation disorders.