Different origins, different hair textures, one shared humanity. Celebrating the natural diversity of human hair. © APPLE & BEARS 2026
Part Two of the APPLE & BEARS Human Hair Series
From follicle architecture to keratin chemistry and inherited genes, discover what gives human hair its remarkable variety of shapes.
Why does one person have straight hair while another has flowing waves, defined spirals or tightly formed coils? Why can siblings have different textures, and why might our own hair change as we grow older?
In Part One, The Origins of Human Hair, we explored hair’s evolutionary history, structure and growth. Here, we look more closely at how each strand acquires its shape.
The answer begins beneath the scalp. Natural texture emerges through the interaction of follicle development, cellular organisation, protein chemistry and genetics, rather than one feature acting alone.
1. The Blueprint Beneath the Scalp: How Curvature Develops
Each hair grows within a follicle extending into the skin. At its base, the hair bulb contains actively dividing cells that contribute to the growing fibre. As these cells mature, they produce structural proteins and undergo keratinisation, forming the resilient material we recognise as hair.
The organisation of this developing tissue helps influence whether the strand grows relatively straight or curved.
Follicles producing curly hair frequently bend within the skin and show asymmetry in their developing structures. Relatively straight hair is commonly associated with a more symmetrical organisation. However, the follicle is not simply a mould through which hair is pushed.
Cells on different sides of a developing fibre can differ in their arrangement, differentiation and protein expression. These differences help create regions with different mechanical properties.
Imagine a flexible strip whose two sides behave differently. Rather than remaining straight, it may bend. A comparable principle helps explain how internal asymmetry contributes to hair curvature, although the biology is considerably more complex.
Researchers continue to investigate how these processes combine across different textures. The central point is that natural curvature develops as the strand forms. Curly hair is not merely straight hair that bends after emerging from the scalp.
From straight to coily, natural hair texture reflects the interaction of follicle architecture, cellular organisation and the developing hair fibre.
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2. The Finished Strand: Geometry, Bending and Twisting
Once formed, a hair fibre has its own geometry and internal structure. Both influence how it bends and twists.
A familiar explanation suggests that round strands are straight and flattened strands are curly. Although cross-sectional geometry is associated with curvature, this is not a reliable rule for predicting an individual strand’s shape.
Human hair can have approximately circular, oval, elliptical or irregular cross-sections. Shape may also vary along a fibre. Two strands with similar cross-sectional dimensions can behave differently because their internal organisation differs.
Much of that organisation lies within the cortex, the main structural region introduced in Part One. Its keratin filaments and associated proteins contribute to strength and flexibility. Differences in their distribution and arrangement can influence bending.
Twisting around the strand’s lengthwise axis, known as torsion, also contributes to its three-dimensional form. A wave, ringlet or coil therefore reflects more than the outline seen in a microscopic cross-section.
The useful distinction is between how a strand develops inside the follicle and how its completed structure behaves. Neither follicle shape nor fibre geometry provides the whole explanation on its own.
3. Keratin Chemistry: Natural Structure and Temporary Styling
Hair consists predominantly of proteins, particularly keratins, organised into a network reinforced by chemical bonds and other interactions.
Disulphide bonds are strong covalent connections formed between cysteine residues within this protein network. They help stabilise the structure created during hair formation.
They do not function as individual switches for straightness or curl. Descriptions suggesting that straight hair has “straight bonds” while curly hair has “angled bonds” reduce a complex structure to a misleading picture.
Hydrogen bonds are weaker interactions that help explain temporary styling. Water changes interactions within the fibre, making it more responsive to reshaping. As hair dries in a new arrangement, interactions reform and help hold that shape.
This is why hair can temporarily retain waves created during drying or appear straighter after styling. Humidity can alter these interactions again, changing the styled result.
Chemical processing works differently. Traditional permanent waving involves breaking and reforming disulphide bonds, while straightening treatments use several different chemical mechanisms. Their effects can persist in the treated length without changing the natural characteristics of new growth.
Natural texture develops in the follicle. Temporary styling rearranges an existing fibre, while chemical processing can alter its internal structure.
Keratin proteins and their chemical bonds help give human hair strength and flexibility. Disulphide bonds stabilise its structure, while hydrogen bonds contribute to temporary changes in shape when hair is exposed to water and styling.
Illustration © 2026 APPLE & BEARS
4. Inherited Variation: Why Siblings Can Have Different Textures
Hair texture is a polygenic trait: multiple genes contribute to its development. It cannot be adequately explained by the familiar classroom model of curly hair being dominant and straight hair recessive.
Each child inherits a different combination of genetic variants. Those combinations influence follicle development, cellular organisation and structural proteins, helping explain why siblings can have noticeably different hair.
Several genes illustrate this complexity.
TCHH provides instructions for trichohyalin, a protein involved in the organisation and reinforcement of structures within the follicle. Studies have associated variation in this region with hair shape, particularly in populations of European ancestry.
EDAR participates in a signalling pathway involved in the development of hair follicles and other structures. A widely studied variant, V370A, has been associated with differences in hair thickness and straightness and occurs at relatively high frequencies in some East Asian populations.
Research has also linked variation involving PRSS53 to hair curvature. These findings identify contributors within a wider biological system, not individual genes that dictate a complete texture.
The frequencies of hair-related variants differ between populations, but texture alone cannot reliably establish someone’s ancestry. Human variation overlaps, and broad labels conceal considerable diversity within families and communities.
Genetics helps explain why texture is inherited without making the outcome a simple or predictable copy of either parent’s hair.
5. The Texture Spectrum: Describing What We See
Straight, wavy, curly and coily are useful descriptions of visible patterns, not four sharply separated biological types.
- Straight: Little visible curvature.
- Wavy: Gentle bends or more pronounced S-shaped patterns.
- Curly: Recognisable loops, spirals or ringlets.
- Coily: Tightly curved spirals, small loops or angular-looking patterns.
A single head can contain more than one of these patterns. Strand length, styling and environmental conditions can also affect how clearly they appear.
One particularly noticeable feature of tightly curved hair is shrinkage. A strand may look much shorter when resting in its natural shape than when gently extended because its length is contained within repeated curves.
Shrinkage does not mean the hair is failing to grow. It describes the difference between the strand’s extended length and the space it occupies in its natural arrangement.
These descriptions help us discuss appearance, but they do not reveal everything about a fibre. Texture does not, by itself, establish strand diameter, strength, condition or how someone’s hair will respond to a particular routine.
6. Why Texture Varies Across the Scalp and Throughout Life
Individual follicles do not necessarily produce identical fibres. Differences in their structure and activity can contribute to mixed textures across the scalp.
Someone may notice looser waves in one area and tighter curls elsewhere. Length, previous styling and damage can further alter the appearance of those patterns. The biological reasons for regional variation are not yet fully understood.
Texture can also change as new hair grows during different stages of life.
During childhood and puberty, follicular maturation and hormonal development can influence hair characteristics. Some people develop more pronounced waves or curls; others notice little change.
Pregnancy and the period after birth are associated with changes in growth cycles and shedding. Some people also report texture changes, although these are less clearly understood than the effects on hair growth.
With ageing, fibre diameter, pigmentation and follicle activity can change. Hair may appear finer, coarser, straighter or more wavy, with no single pattern applying to everyone.
Certain medications and medical treatments can also affect new growth. Curls appearing after chemotherapy, sometimes called “chemo curls”, are one recognised example and may be temporary.
These observations reflect an important distinction: inherited DNA generally remains stable, but gene activity and follicle behaviour can change. The follicle is a living system, not an unchanging factory.
Significant or unexplained changes, especially alongside hair loss or scalp symptoms, should be discussed with a qualified healthcare professional.
7. What Texture Means for Hair Care
Understanding texture can help explain grooming behaviour, but a useful routine also considers strand diameter, density, scalp condition, chemical processing and existing damage.
Sebum, produced by glands associated with follicles, lubricates the scalp and contributes to the hair’s surface condition. Its distribution along a fibre can be affected by curvature and grooming. Some people with highly curved hair notice oilier roots and drier-feeling ends, but scalp oiliness and the condition of the lengths are separate considerations.
Friction is another important factor. Neighbouring strands rub against one another during washing, drying, combing and styling. Tangles and forceful detangling can increase mechanical stress, while repeated wear can damage the protective cuticle.
Highly curved fibres may experience concentrated stress at bends, but curl pattern alone does not determine breaking strength. Diameter, internal structure, weathering and chemical damage also matter.
Conditioning can reduce friction and improve manageability. Gentle handling, limiting unnecessary pulling and adjusting detangling to the individual’s hair can help reduce avoidable damage.
It is also useful to distinguish the opening of a curl from stretching the fibre itself. A coiled strand initially lengthens as its curves straighten; further tension places increasing stress on the material. Visible springiness is not proof that hair can tolerate unlimited stretching.
Different textures can present different practical demands. Recognising those differences does not mean ranking one as healthier or better than another.
The aim is not to make every texture behave alike, but to choose care that suits the individual hair and scalp.
The Beauty of Human Variation
Hair texture is the visible expression of processes we rarely see: cells organising beneath the skin, proteins forming resilient structures and inherited variation influencing each new strand.
Understanding those processes replaces simple assumptions with a richer appreciation of difference. Straightness, waves, curls and coils are not competing standards. They are varied expressions of the same remarkable human biology.
At APPLE & BEARS, we believe that appreciating this diversity begins with understanding it.
Our hair does not need to look the same to be equally extraordinary.
Coming Next in the Human Hair Series
Shape is only part of the story. What makes hair black, brown, blonde or red, and why does its colour change with age?
Part Three: The Palette of the Strand will explore melanin, natural hair colour and the biology of grey, silver and white hair.
Scientific References and Further Reading
- Westgate, G. E., Ginger, R. S. & Green, M. R. (2017). The biology and genetics of curly hair. Experimental Dermatology, 26(6), 483–490. Read the review on PubMed.
- Wortmann, F. J. and colleagues (2020). Why is hair curly?—Deductions from the structure and the biomechanics of the mature hair shaft. Experimental Dermatology, 29(3), 366–372. Read the research.
- Liu, F. and colleagues (2018). Meta-analysis of genome-wide association studies identifies 8 novel loci involved in shape variation of human head hair. Human Molecular Genetics. Read the full research article.
- MedlinePlus Genetics, US National Library of Medicine. Is hair texture determined by genetics? Read the genetics explanation.
- MedlinePlus Genetics, US National Library of Medicine. EDAR gene. Read the gene summary.
- MedlinePlus Genetics, US National Library of Medicine. TCHH gene. Read the gene summary.
- Nissimov, J. N. & Das Chaudhuri, A. B. (2014). Hair curvature: a natural dialectic and review. Biological Reviews, 89(3), 723–766. Read the review on PubMed.
Editorial Disclaimer
The APPLE & BEARS Human Hair Series is published for general educational and informational purposes and is informed by published scientific research and academic sources.
APPLE & BEARS is a British beauty and body-care brand, not a medical authority. This content should not be regarded as professional medical advice, diagnosis or treatment.
Readers experiencing concerns about scalp health, significant hair changes or hair loss should consult a qualified healthcare professional.
© 2026 APPLE & BEARS. All rights reserved.
