Funny how we’ve shed most the the hair on ours bodies, yet us obsess for this reason much around the strands that remain… picture by kyle blacksmith on Unsplash

Humans, uneven apes and our various other closest types relatives, are relatively hairless. This is largely welcomed to be an adaptation to moving away indigenous shady forests and out right into the open up savannah, where less hair enabled us to far better regulate our temperature through sweating.

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“Relatively” is the vital word there, however. Us still retained the hair on our heads, and we still have hair follicles spread across our body to differing degrees, on ours arms, legs, and also torso.

But this hairs don’t flourish in the same means as those on our head. While ours head hair can thrive to an ext than 2 or 3 feet in length, my eight hairs have never made that past half an inch, despite never being trimmed.

Why nothing these hairs flourish the very same way? Why go the hair on ours head thrive so much much longer than any type of others?

And what’s the objective of our remaining hair, quiet — both the hair on our head, and also the hair in other body areas?

Let’s discover some science and also tackle this hairy (sorry) questions!

How our Hair knows to Grow

Each among our hairs grows from a committed little cluster of cells in our skin, referred to as a follicle. And also each follicle go through three phases that growth, although different follicles space in various phases at various times.

Here are the three phases of hair growth:

The Anagen Phase

This is the growth phase because that hair! if the follicle is in this stage, that producing brand-new hair, growing at a price of approximately 1 centimeter per month. The much longer that a single follicle remains in the anagen phase, the much longer the hair being created by the follicle will grow.


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The Catagen Phase

This is the transitional phase, as the hair follicle move from energetic to inactive. For about two weeks, the hair stops growing as the follicle shrinks and also disintegrates in order to renew itself. The hair might seem to prosper a tiny small bit, but it’s not actually gaining longer — simply rising up closer come the surface.

The Telogen Phase

And now, i sleep. This is the dormant phase of a hair follicle, wherein the hair is anchored in place, yet doesn’t grow any kind of longer. This conservation the hair without the human body spending added resources top top it.

Near the finish of the telogen phase, the anchors that host the hair in place will loosen, and also the hair will fall out. Soon, within a couple of weeks, a new hair will certainly form, and the follicle will transition back to the anagen phase.

So, our hair follicles go:

Anagen -> Catagen -> Telogen -> Anagen…

And the an enig to why the hair on our head room much longer than the hair on our arms and also legs rests in exactly how these phases different in different areas of our body.


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I know what she thinking. “Why i will not ~ my arm hair thrive as luxurious and also long as my head hair, no matter exactly how much I treatment for it? ok never attract a partner if ns can’t gain some glossy, long armpit hair!” picture by billie on UnsplashHair Length: the All around That Anagen (Phase)

All the hair follicles ~ above our body go through these 3 phases, yet head hair follicles are various — lock spend much longer in the anagen phase, while hair in other areas spend much more time in the telogen phase.

All the hairs flourish at about the same rate, yet the hair on ours head keep growing for months to year at a time, i m sorry is how they get so long. Meanwhile, the hair on ours arms and legs are only programmed to thrive in the anagen phase because that a pair of months — therefore they only acquire a little length before they protect against extending.

And remember, this cycle isn’t aligned for each follicle! One follicle may be simply entering the anagen phase, while another follicle — even one right nearby — may be in the catagen or telogen phase.

This explains why, regardless of each hair acquisition as long as a year come grow, we still it seems ~ to melted hairs constantly! We’ve got around 100,000 hair on our head, so that even if the rate of expansion is evenly averaged across all the them, we’d shed around 274 hair a day.

One other exciting note is that we additionally shed our other hairs, choose our arm and also leg hairs! However, because these hair are shorter and smaller, we are less likely to an alert them piling up on our sheets or floor.


But Why Hair at All? Why no Smooth and also Pristine?

After all this discussion about the energy we invest on growing and maintaining our staying hairs, you might wonder: why perform we require hair at all? Shouldn’t us no much longer need any type of hair, currently that we’ve created the indoor thermostat?

In fact, ours hair does still have actually some cool purposes! there are reasons why our body keeps it around.

The hair on our head helps to safeguard our scalp indigenous UV radiation. As anyone that is bald (or has actually shaved their head at some point) can likely attest, the scalp is rather sensitive to the sun and can easily end up being sunburned. Our head hair helps us prevent that irritation.

The hair on our head additionally helps lock in warmth in cold environments, and also can assist provide extr surface area because that our sweat to evaporate in hot settings to cool united state off.

And what about the hair on the remainder of our body? the serves a purpose, as well.

Hair in our armpits and crotch help reduce the amount of skin-on-skin friction, to prevent friction burns. This hair also helps us store cool, through providing an ext surface area for our sweat to evaporate. Finally, hair in our pubic areas can help keep us pathogen free, by staying clear of foreign substances from straight touching the skin.

None that these advantages is life-or-death, so we have the right to live without our body hair (and indeed, it’s come to be a fashion declare in many areas). However, because that those who select to save their human body hair, that got advantages besides laziness!


It occasionally seems choose our body can magically sense how long our hair is, and also stop it growing in some locations while permitting it to proceed in others.

In fact, the truth is the the hair on our head security a far longer duration of time in the expansion phase, or anagen phase, if the hair ~ above the rest of our human body spends many of its time in the dormant telogen phase.

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And the hairs us grow, no issue where lock are, offer a purpose, whether it is protecting united state from the sun, help to keep us warmth or cool, reducing friction, or offering defense against pathogens.

Now, if I might just evolve the capacity to readjust the color of mine hair by concentrating… come on, Evolution!