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How many hairs does the human head have? Some quirky facts about hair

8.10.2022

What determines whether hair is light or dark and are blondes really a dying breed? In the first of two parts, we provide the answers to these and other hairy questions.

It’s just hair. In other words, cutaneous appendages. That’s how biologists refer to the stuff that grows on our heads. After all, hair is made of the same material as horns and toenails – and is nothing more than dead cells... Oooops. I think I just gave all of you hair-lovers the shock of your lives. Yeah, to a lot of people, hair means everything. Hair means sexiness and power, and those who lose it often lose a fair amount of self-confidence to boot.

Since we all have hair, the topic is quite relevant – so let’s take a closer look at the questions involving our crowning glory.

The most important question first: why do we have hair?

Our body hair serves several purposes. To start off, hair provides a bit of warmth, and special tactile hairs enhance our sense of touch. Hair protects us from harmful UV radiation and infrared light by absorbing them. Hair also helps us spread pheromones. And last but not least, hair wicks away excess moisture.

How many hairs does the human head have?

That’s not so easy to answer. First of all, not all hair is the same. Everyone’s hair differs in structure, density, thickness and colour. How fast a person’s hair grows and the number of hairs on a head is no different – it depends on the person. Nevertheless, hair colour has an effect on the approximate number of hairs on a person’s head. Redheads, on average, have the fewest – around 75,000. Blonds, on the other hand, are at the top of the podium with 150,000 hairs. People with brown and black hair rank about the same with 100,000 to 110,000 hairs.

Not only are redheads rare, but so are (natural) blonds. Together, they make up only about four percent of the world’s population, writes Gerhard Staguhn in his book «Und ewig lockt das Haar». The vast majority of people have either brown or black hair.

What determines whether a person has blond, brown, red or black hair?

Only two pigments are responsible – albeit in different ratios – for hair colour: eumelanin and pheomelanin. Both pigments are also called melanins. A lot of eumelanin results in dark brown to black coloration, a lot of pheomelanin in orange or red coloration. Blonds have very little of either pigment.

In the scientific world, blond is sometimes not considered a hair colour of its own but rather a variation of red, because both produce little eumelanin. How blond coloration developed, researchers don’t yet know for sure. But that’s not the case for red (blond) coloration. It’s known to have resulted from a mutation of the melanocortin-1 receptor (MC1R). As a result, MC1R produces less of the dark eumelanin pigment. In 1995, British researcher Jonathan Rees first published this theory on red hair in a study.

Why does hair turn grey?

Scientists found in 2009 that the greying of our hair is related to the presence of a substance that artificial blonds know all too well – hydrogen peroxide (H2O2). It’s a by-product of the metabolism and is permanently produced in small quantities, even in hair. In particular in the hair root, which is surrounded by the hair follicle and where the colour pigment melanin is produced.

While we’re young, the body easily breaks down the «bleaching agent» hydrogen peroxide into its individual components hydrogen (H2) and oxygen (O2) – thanks to an enzyme called catalase. But we produce less and less of it as we age. The result: hydrogen peroxide ends up bleaching our hair naturally. This is because the hydrogen peroxide that becomes available attacks the enzyme tyrosinase, which is essential for the production of the hair pigments eumelanin and pheomelanin in the hair follicles.

That was a lot of foreign words, so let’s re-cap: because the body can no longer break down and neutralise hydrogen peroxide in old age, the hydrogen peroxide inhibits the production of melanin, which colours hair.

If hair grows back, what’s deposited is no longer melanin but small air bubbles. That’s what makes our hair look white. By the way, if you’ve ever referred to hair as grey, you’re under an optical illusion. In reality, the air bubbles turn our formerly coloured hair into pigmentless hair, i.e. white hair. But as long as our heads are still covered with fully pigmented hairs for the most part, they overlap with the colourless hairs. This creates the impression of grey hair.

Are blonds dying out?

There are few people in the world who are naturally blond. Blonds are even said to be dying out. This theory has been around since 1865 and is re-visited again and again by scientists, according to the U.S. fact-checking website snopes.com. The reason for dwindling blonds? Hair coloration is determined by dominant-recessive genes. This means that darker, dominant hair colours usually prevail over lighter, recessive ones. If a child inherits the gene for dark hair from one parent and the gene for blond hair from the other, the dark gene wins out. The blond gene only asserts itself when it’s passed on from both parents.

Many people have both the dark and blond genes in their make-up. In other words, dark-haired parents can also pass on the blond gene. But their child will only be blond if both parents pass on the blond gene to the child. If both parents carry the blond and the dark-haired gene, the chance of blond offspring is 25 per cent.

So are blonds dying out? No, Jonathan Rees, professor of dermatology at the University of Edinburgh (the MCR1 researcher), tells BBC News. The genes for blond hair are still passed on, even if the dark gene usually prevails. «The only reason blondes would disappear is if having the gene was a disadvantage and I do not think that is the case. The frequency of blondes may drop but they won't disappear.»

PS Anyone who was born with blond hair will eventually lose this colouring by early adulthood. Blond hair darkens with age because the brown-black pigment eumelanin begins to assert itself, whereas in childhood it’s still the red-blond pigment phaeomelanin that’s dominating.

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Annalina Jegg

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oliver.fischer@digitecgalaxus.ch

The adjectives that describe me? Open-minded, pensive, curious, agnostic, solitude-loving, ironic and, of course, breathtaking.
Writing is my calling. I wrote fairytales age 8. «Supercool» song lyrics nobody ever got to hear age 15 and a travel blog in my mid-20s. Today, I’m dedicated to poems and writing the best articles of all time.

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