Just how much do you know about your hair?

You already know from part 1 of this hair trivia series that blonds aren’t dying out and that grey hair isn’t really grey at all. In this second article, we’ll start with one of the most frequently asked questions about hair.

How fast does hair grow?

Gerhard Staguhn wrote, in his book about hair «Und ewig lockt das Haar»: «Once a strand of hair has finished growing, (...) the end attached to the papilla shrinks and detaches itself. After a certain period of «rest», a new strand begins growing in its place – in the same channel beneath the scalp. As the new hair grows upward, it pushes the old hair up until it falls out.» How quickly does this happen, you ask? Well, after bone marrow, hair is the second fastest growing tissue in our body. Hair grows 0.3 to 0.5 mm per day, and up to 15 centimetres a year.

But how fast hair grows depends on factors like age and gender. They come into play during the hair cycle, which can be divided into three phases. In the so-called anagen phase, a new hair root is formed and the production (i.e. growth) of a strand of hair is underway. Depending on age and gender, it can last anywhere from two to six years. In the catagen phase, which lasts about two to three weeks, the hair follicle at the lower end narrows and shortens; the hair atrophies. In the final phase, the telogen phase, the dermal papilla and the hair follicle are regenerated; a new strand of hair is formed. The process takes two to four months.

Why do so many men (and some women) go bald?

Hair loss can occur for various reasons. Take diffuse hair loss, i.e. when hair falls out fairly evenly across your head, which can be a side effect of medication. The cause of circular hair loss, however, is not yet conclusive. This balding, known as androgenetic hair loss or androgenetic alopecia (AGA), is often experienced by people in their later years. It affects about 80 per cent of men worldwide. And according to one study, it affects up to 50 per cent of women. Hair becomes thinner and grows back shorter because its growth phase is shortened. The cause is a hypersensitivity of the hair follicles to the steroid hormone dihydrotestosterone (DHT). AGA is also known as hereditary hair loss because how sensitive your hair roots are to DHT is determined by your genetics.

How strong is our hair?

Hair is worth heralding – at least when it comes to natural strength. Just 500 to 1,000 strands of your hair could support the weight of a person, without snapping. This is partly due to the complex structure of hair. Every strand of hair is covered by an outer «cuticle» layer and consists of bundles of fibres, known as the cortex. These bundles are composed of keratin fibres called fibrils. And even smaller keratin fibres are, in turn, embedded in the fibrils. This makes our hair incredibly resistant to tearing.

Surprising fact: the thinner a strand of hair, the stronger it is. That’s what researchers concluded after carrying out a study comparing hair samples from humans and animals. Why is thinner hair stronger? Scientists investigated this question with the help of a stress test. The findings? Thick hair breaks differently than thin hair. While strands of hair with a diameter of 0.2 millimetres or greater break relatively cleanly, thinner strands of hair (which we humans have) break unevenly. That’s why they can hold more weight.

And the best for last – it turns out hair can save our oceans!

Hair binds fats. This property of hair can benefit the environment if we harness it to purify our seas. Hair acts as a natural sponge when contaminants such as gasoline, oil and sunscreen are present in bodies of water. This means that in addition to decreasing waste by the tonnes, hair salons could give hair a whole new purpose if they were to save their daily clippings instead of dumping them in the trash.

The Hair Help the Oceans initiative is encouraging hairdressers to do just that. The project is currently ongoing in Switzerland, Austria and the Netherlands. It’s been modelled after the association «Coiffeure Justes» (fair hairdressers), based in the south of France. They fill old nylon stockings with hair, roll them up, and tie them tight. Add a cork so that the stocking doesn’t sink, and presto – you’ve got a sea-fit hair filter! Such a filter can even be reused up to eight times. That’s how one kilo of hair can filter almost eight kilos of oil out of the water. In 2019, hair filters of this kind were put to use when an oil freighter capsized off the coast of Mauritius, releasing thousands of tonnes of oil into an area covering about 30 square kilometres.