Why do we have coily hair? The playground question, finally answered

In the school playground, a classmate puts her hand on your head: why does your hair do that? Years later, the question comes back in front of the mirror, and less kindly.

The answer lies in something tiny, buried under the skin of your scalp, that decides everything before the hair even appears. That one mechanism explains dryness, fragility and volume all at once, and it makes sense of gestures that once seemed arbitrary. For the practical side, our step-by-step tutorial walks you through the six steps of the Rituel Texture®.

OriginIt all happens in the follicle

The hair follicle is a tiny pocket set into the scalp. It's what makes the hair fibre, and its shape decides the shape of the hair. A round pocket, set in straight, produces straight hair. An oval, curved pocket produces a curl, tighter the flatter the oval. A very elliptical pocket, set in at an angle, produces coily hair, which emerges almost parallel to the skin and starts coiling within the first few millimetres.

This shape isn't acquired along the way. Studies on follicles isolated and grown in the lab have shown that the curvature is already built into the bulb, before the fibre even emerges (Thibaut et al., British Journal of Dermatology, 2005). No treatment and no device can change texture at its source. What you can change, and that's already a lot, is the condition the fibre is in as the years go by.

The cross-section of the fibre follows the same logic: where straight hair is almost round, coily hair is oval, often distinctly flattened, and its curvature changes several times along a single strand (Khumalo et al., Journal of the American Academy of Dermatology, 2000). Those twists are what give the hair its volume, and why it fills the space around it instead of falling flat.

Consequence 1A fibre that's dry by design

The scalp produces sebum, an oily substance that protects the skin and lubricates the hair fibre. On straight hair, it travels down unhindered and reaches the ends within a few days: that's why straight hair gets greasy quickly. On a coily fibre, it has to get round every bend of the spiral and stops well before the end.

Hence something many women know without ever having read it anywhere: roots that get greasy within days and lengths that stay dry, on the same head, at the same time. So dryness in coily hair isn't a sign of poor care. It's the direct result of its geometry, and it means bringing in regularly, from the outside, what the scalp can't spread on its own. See why coily hair is often dry.

That changes how you judge a product: a cream that only “lasts” two days isn't breaking its promise. It's meeting a fibre that loses water fast and is better topped up at regular intervals than coated more heavily.

Consequence 2Where the fibre gives way

Every bend is a weak point. Where the spiral turns, the fibre is thinner and flatter, and the keratin is spread less evenly. That's almost always where hair breaks, and where knots form, as one strand catches in the twist of another.

People often jump to the wrong conclusion: that you should never touch your hair when it's dry. It's the opposite. What causes breakage is a comb dragged through dry hair with no product, forcing its way through every twist instead of undoing it. Detangling with your fingers, on the other hand, works well on dry hair: it's step 01 of the Rituel Texture®, Chadian finger detangling, and it's precisely because the fibre is fragile that it's done by hand. Le Peigne de Man Dol' comes in at step 04, on hair coated in Le Masque Réparateur, when the fibre glides. We come back to this mix-up in our six myths about coily hair.

OriginsWhat climate explains, and what it doesn't

Why did this follicle shape spread in some places rather than others? The most widely discussed hypothesis is about heat: very tightly curled hair would shield the scalp from the sun's rays while letting air circulate at the roots. It was put to the test in 2023 by exposing a thermal mannequin, wearing wigs of different textures, to calibrated radiation: the curlier the texture, the less heat reached the scalp (Lasisi et al., Proceedings of the National Academy of Sciences, 2023).

So the hypothesis holds up, and it places this texture among the finely evolved forms rather than the accidents. But it should be handled with care: a lab experiment measures an effect, it doesn't tell the story of a population. Textures aren't spread across a map as neatly as is sometimes claimed, families have long mixed different origins, and two sisters don't necessarily share the same pattern. Above all, this very ancient story says nothing about what your hair needs this weekend.

Reference points3A, 4B, 4C: what these codes are worth

You've definitely come across them. This classification was created in the 1990s by an American hairdresser, initially to go with a line of hair products, before spreading far beyond it. It sorts hair into four families, from straightest to coiliest, each split into A, B and C, and it did women a real service by giving them a vocabulary they'd never had.

Researchers, though, don't work in letters. They measure the diameter of the curl, the curvature of the fibre and the number of waves over a given length, which gives a continuous scale rather than boxes (Loussouarn et al., International Journal of Dermatology, 2007). Between 4A and 4B there's no border, just a gradual shift.

Two limits are worth knowing. A single head often has several patterns, and the nape is almost never the same texture as the crown. Above all, knowing you're 4B tells you nothing about what to put on your hair: porosity and density count for far more. They're what we look at first during a hair diagnosis.

In practiceWhat it changes in the way you care for your hair

Once you accept that the fibre is dry by design and fragile at every bend, most decisions make themselves. Three principles are enough.

Water always comes first

Moisturising means bringing in water, and nothing else. Oil applied to a dehydrated fibre doesn't rehydrate it: it locks in whatever state it's in. In the Rituel Texture®, water comes in with the wash and with Le Masque Réparateur, left on for ten minutes, then La Crème Coiffante helps hold on to that moisture. A drop of light oil can be added to the ends between routines. See moisturising coily hair.

Hands before tools

Since the fibre gives way at the bends, it's handling that decides breakage, long before what's in your products. That's why the Rituel Texture® starts with your fingers, on dry hair, section by section, and tools only come in once the fibre is coated in treatment. See our method for detangling without breakage.

And then there's the night

A night of rubbing against cotton damages your lengths without you noticing, always in the same places. Ghana prefers a silk scarf, with a silk pillowcase, and six braids twisted in on themselves, never tight at the root. Our night-time hairstyles sort it out in a few minutes.

HeritageA texture that carries a history

The question “why do we have coily hair?” is never purely biological. This texture has been commented on, straightened and hidden before being claimed with pride, and many women learned to talk about it as a problem before understanding how it works. Knowing what goes on beneath your scalp means no longer measuring yourself against a model that was never yours.

That history can be read in hairstyles. African braids have carried belonging, and sometimes escape routes. Himba women's hairstyles still tell the age and status of the woman wearing them. And in France, well-known figures wear their afro without having to explain themselves.

Frequently asked questions

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Sources

• Thibaut S. et al., “Human hair shape is programmed from the bulb”, British Journal of Dermatology, 2005.
• Khumalo N. P. et al., “What is normal black African hair? A light and scanning electron-microscopic study”, Journal of the American Academy of Dermatology, 2000.
• Loussouarn G. et al., “Worldwide diversity of hair curliness: a new method of assessment”, International Journal of Dermatology, 2007.
• Lasisi T. et al., “Human scalp hair as a thermoregulatory adaptation”, Proceedings of the National Academy of Sciences, 2023.