CURL SCIENCE / TEXTURE
Every spiral, wave and coil starts forming long before your hair meets a curl cream. The real story begins inside the follicle.
Your curl cream would like some credit.
Your gel would like even more.
But the reason your hair curls begins before either of them enters the bathroom.
A strand is already being given its characteristic shape while it is growing inside your scalp, where follicle geometry, the developing hair fibre and the organization of cells within that fibre all help determine whether it emerges relatively straight, gently curved or wrapped into a much tighter curl.
Scientists have spent decades looking at curls under microscopes, growing follicles in laboratories and, more recently, reconstructing entire hair fibres in three dimensions.
The conclusion is more interesting than “curly hair has an oval shape.”
A curl is the visible result of asymmetry, geometry and biology working together along an extraordinarily small fibre.
The curl starts inside the follicle
One of the clearest clues came from researchers who examined curly hair follicles themselves.
Instead of finding a perfectly straight tube producing a fibre that somehow decided to curl later, they found curved follicles with asymmetry in the bulb and surrounding structures. The cells responsible for producing the growing hair were not behaving identically on both sides.
Even more convincingly, when curly follicles were removed and maintained in laboratory culture, the new fibres they produced stayed curved.
That tells us the curl is being programmed during growth.
The asymmetry continues into the developing hair shaft. Research comparing straight through tightly curled fibres has found differences in cortical organization and keratin distribution, with curly fibres showing asymmetric patterns that correspond with the direction of curvature.
Imagine trying to build a perfectly straight ribbon while one side of the developing structure is behaving slightly differently from the other.
You can start to see where the bend comes from.
The follicle can be curved.
The growing fibre can develop asymmetrically.
The cortex can differ from one side of the strand to the other.
The fibre can rotate and change curvature along its length.
By the time you see the strand above your scalp, a lot has already happened.
No, it is not just “round hair versus oval hair”
You have probably heard the tidy explanation that straight hair is round and curly hair is oval.
There is some truth hiding inside that simplification. Research has found relationships between curl and the cross-sectional geometry of hair fibres, with curlier fibres often showing more elliptical characteristics.
But a two-dimensional cross section cannot tell the whole story.
A 2025 micro-computed tomography study reconstructed human hair fibres in three dimensions and examined features such as cross-sectional shape, rotation and variability along the fibre. The researchers found considerable complexity, including variability within individual hairs.
That matters because a curl is not a static oval sitting on a microscope slide. It is a long three-dimensional structure bending, rotating and changing direction through space.
Which is also why two strands that look similar from across the room can behave quite differently once you wash, stretch or style them.
Hair texture is geometry with a very good publicist.
Your curl pattern is a spectrum, not a set of tiny boxes
Humans really enjoy categories. Hair did not get the memo.
In a worldwide study of more than 1,400 people across 18 countries, researchers measured physical characteristics such as curve diameter, curl index and the number of waves rather than relying on ethnicity. The work showed enormous variation in hair shape and created eight broad categories to describe that continuum.
Even those eight categories are a system humans imposed on continuous biological variation.
More recent researchers have continued to point out how much variability exists both between people and within individual fibres.
That is why a chart can be useful for saying, “My hair generally looks something like this,” but much less useful when it becomes, “Therefore I am required to use exactly these four products.”
Your curl pattern tells us about shape.
It does not automatically tell us your density, porosity, strand diameter, damage history or what level of hold you enjoy.
Your curl pattern can describe the shape of your hair. It cannot describe everything your hair needs.
Water can change the curl without changing the curl pattern
Now we get to the part you witness every wash day.
Your dry curls get wet and stretch. You brush them. They look longer. They clump into a new shape. Then as they dry, the curl returns.
That happens because some of the interactions holding keratin structures together are temporary enough to be influenced by water.
Researchers at the University of Cape Town recently found preliminary evidence supporting the role of weak hydrogen bonds in temporary shape changes of curly human hair.
This is why water can help you reset yesterday’s bent curl or why drying hair in a stretched arrangement can temporarily change how the curl presents itself.
It is also why humidity can join the styling conversation without being invited.
Hair takes up water from the environment, and humidity changes its mechanical behaviour. A beautifully shaped curl can soften, expand or shift as environmental conditions change.
None of that means your follicle suddenly changed its mind.
The underlying fibre still has the natural geometry it was given during formation.
Then why can heat or chemicals make a curl look different?
Because once the fibre leaves your scalp, you can alter the material even though you cannot change the follicle that produced it.
Water and temporary styling usually change weaker interactions that can reform. Chemical straighteners work much more aggressively by altering stronger bonds within keratin. Bleaching, colouring and repeated high heat can damage structural components of the fibre as well.
That is why someone can have tightly curling new growth and straighter older lengths.
The follicle is still producing the original pattern. The older hair has simply had a different life.
This distinction is also why damaged curls cannot always be persuaded completely back into their original shape with conditioner. Cosmetic treatments can make weathered fibres softer, smoother and easier to manage, but a seriously altered strand may remain altered until it is eventually cut away.
Your next centimetre of new growth, however, starts the process again at the follicle.
And yes, one head can make a whole curl collection
Once you understand how much geometry and biological variation go into a single fibre, mixed curl patterns start to feel much less mysterious.
Your thousands of follicles are not one machine stamping out identical copies. Individual fibres can vary in shape, diameter and curvature. Different regions of your hair can also have different lengths and histories of heat, colour, friction and environmental exposure.
That loose section around your crown and the tiny spirals at your nape can both be yours.
You do not need to choose which one represents your “real” hair.
And you definitely do not need to make them identical before the wash day counts as successful.
The most interesting thing about curls may be that their complexity survives every attempt we make to squeeze them into a simple diagram.
A curl is not just a shape sitting on your head. It is a tiny record of how that fibre was built, how it grew and everything that happened to it afterward.
Disclaimer: This article provides general hair-care information and is not a substitute for advice from a dermatologist or other qualified healthcare professional. Persistent breakage, scalp changes or sudden hair loss should be evaluated by a healthcare professional.