Why do we get grey hairs?

Beatriz Sevilla decided to stop colouring her hair on her 58th birthday, a couple of years ago. "I didn't have many grey hairs, but I was tired of having to colour it every few weeks. Two of my friends had let their hair go grey naturally and I thought it looked great, so I decided to do the same," says Beatriz, who works as a secretary.

It is fashionable nowadays to leave hair to go grey, but why do we have grey hairs in the first place? Are they hereditary? And is it true that if you pull one out three others will grow in their place? David Saceda, a dermatologist with the Trichology Group of the Spanish Dermatology and Venereology Association (AEDV), answers our questions about those silvery grey hairs that often bother us so much.

Not grey or white - transparent

In reality, a grey hair is simply a hair that has lost its natural colour. It doesn't turn grey, it just isn't black, brown or blonde any more.

"If you look at a grey hair under a microscope, you will see that it is transparent. What happens is that the structure of the hair and the way the light shines on it makes it look grey or white," says Dr Saceda.

Something else can also occur when grey hairs are damaged, for example from the chlorine in a swimming pool, the use of unsuitable shampoos or contamination: they appear more yellowy in colour. "That's why it is always best to use products which are designed specifically for grey hair," he says.

Why does hair lose its colour? Because the melanocytes - the cells which give our skin and hair their colour - continue to produce melanin until, over time, it runs out. "We also know that the melanocytes of the hair are much more sensitive than those of the skin, and that's why our skin doesn't lose its colour but our hair does," says Dr Saceda.

It is a process which is highly determined by genetics, because if your father or mother goes grey at a young age, it is highly likely that you will as well. However, there are other factors which can accelerate or slow down - but not stop - the process.

"These are basically the same as those that favour ageing. Bad lifestyle habits, such as a diet lacking in vitamins and antioxidants and high in saturated fats, not taking exercise, drinking alcohol... all these increase oxidative stress in our body, and make our skin and hair age more quickly".

Starting at the temples

Genetics plays a determining role in greying hair, much more than any other aspect. The way you look after yourself can reduce or delay their appearance, "but when you see someone very young with grey hair or an older person without any, that is due to pure genetics," says the doctor.

He also explains that some people have a white streak in their hair while the rest is their normal colour, and this is usually something that occurs at birth because there are no melanocytes in the area of the skin where the hair emerges.

This is not like the traditional type of grey or white hair, which is scattered all over the head. Generally, the first ones appear around the temples - especially in men - and then spread over the rest of the scalp. White hair on the body or in the beard follows the same process as on the head. There is no difference, except they normally appear a bit later.

The myth about pulling out

How often have we heard that old wives' tale, that if you pull a grey hair out three will grow in its place? Because it isn't true. "Pulling out a grey hair doesn't affect any of the others. They will grow in their own time," says trichologist David Saceda.

Are the grey hairs coarser than the rest? Yes, that bit is true. "As we age, our grey hairs are a bit thicker than the rest and can even appear to stand out more. That's because they tend to be curlier and frizzier".

Is it true that stress can make hair go grey? This year scientists have discovered that there is a direct relationship between stress and grey hair. Until now, nobody had known for certain, but they have discovered that it is the case. Stress can cause grey hairs due to two mechanisms. One is hormonal, for example the mechanism that produces the adrenalin that we all know and have experienced, and cortisol. These hormones increase with stress and have a negative effect on the hair. There is also a direct relationship with the central nervous system. There are nerve fibres which reach just to the base of the hair and they know when we are under continual and constant stress. This can affect the melanocyte early, so grey hairs appear. In fact, it is very common for something like a divorce or death in the family to result in hair going grey within two or three years.

When Barack Obama became president, experts monitored him to see how his hair colour changed from the time he took office to the end of his second term, and the difference was very noticeable. "Until recently it had not been scientifically proven whether the grey hair appears just as a result of time passing or because of stress, but there is no longer any doubt about that. Stress is an important factor," says Dr Saceda.