Hair can be pin-straight, loosely wavy, tightly curled, coiled, or somewhere in between. Even within a single head of hair, curl patterns can vary significantly from one area to another. But what actually determines whether hair grows straight, wavy, curly, or coily?
The answer begins below the surface of the scalp. Genetics, the shape and structure of the hair follicle, the shape of the hair shaft, and the chemical bonds within the hair all contribute to curl pattern. Hormonal changes, aging, hair damage, and environmental factors can also influence how that natural pattern looks over time.
Understanding these factors can help explain not only why different people have different hair textures, but also why your own curl pattern may change throughout your life.
Hair Curl Pattern Starts With Genetics
Genetics plays a major role in determining natural hair texture. Hair characteristics are complex traits influenced by multiple genes rather than one simple “curly hair gene.” The genetic variants inherited from both sides of a family can influence characteristics such as:
- Hair follicle shape
- Hair shaft structure
- Curl diameter
- Hair thickness
- Density
- Growth characteristics
This helps explain why hair texture can vary considerably among family members. Siblings who have the same parents, for example, may have noticeably different curl patterns because they inherit different combinations of genetic variants.
Genetics plays a major role in determining natural hair texture. In fact, a twin study examining hair curliness found that genetic factors may account for an estimated 85–95% of variation in hair curliness among people of European ancestry.
Hair characteristics are complex traits influenced by multiple genes rather than one simple “curly hair gene.” Large genetic studies support this complexity. One study involving 28,964 participants across nine cohorts identified eight new genetic loci associated with human hair shape while confirming several previously identified loci.
The Shape of the Hair Follicle Matters
One of the most important influences on curl pattern is the shape of the hair follicle. The follicle is the small structure within the skin from which each strand of hair grows. Its shape and the angle at which the hair emerges help influence the eventual shape of the strand.
Curved hair is also far from unusual. Research examining hair phenotypes across European, African, Asian, and admixed populations found that more than 50% of hair fibers displayed some degree of curl. Studies of follicle structure have also found that curly hair tends to grow from curved follicles, while straighter hair is associated with more linear follicles.
Generally:
- More symmetrical follicles tend to produce straighter hair.
- More curved or asymmetrical follicles tend to produce wavy or curly hair.
- Greater follicular curvature can contribute to tighter curls and coils.
The process is more complex than simply having a “round” or “oval” follicle, however. Researchers have found that differences in cellular activity and protein distribution within curved follicles also contribute to the bending and curvature of the growing hair fiber. In other words, curl begins while the hair is actually being formed inside the follicle.
Hair Shaft Shape Also Influences Curl
Once hair emerges from the scalp, the physical structure of the hair shaft contributes to its appearance. A hair fiber contains several layers.
Cuticle
The cuticle is the protective outer layer of the hair shaft. It consists of overlapping cells that help protect the inner structures of the hair.
Cortex
The cortex makes up most of the hair fiber and contains keratin proteins as well as melanin, which contributes to hair color. The organization of cells and proteins within the cortex is particularly important to the shape of the hair fiber.
Research suggests that differences in the distribution of cortical cell types and keratin proteins across a hair fiber can contribute to curvature. When growth and structural properties are uneven across the fiber, the strand can bend rather than grow straight.
Keratin and Chemical Bonds Help Hair Hold Its Shape
Hair consists primarily of a structural protein called keratin. Within keratin are chemical bonds that help give hair its strength and shape. One particularly important type is the disulfide bond.
Disulfide bonds form between sulfur-containing cysteine molecules within keratin proteins. The number and arrangement of these bonds contribute to the structure of the hair fiber. This is also why chemical treatments can alter curl pattern. Permanent waving and chemical straightening processes work by disrupting and rearranging bonds within the hair. The hair can then be reshaped into a straighter or curlier configuration. These treatments change the structure of the existing hair shaft. They do not necessarily change the underlying follicle, which means new hair typically continues growing according to its genetically determined pattern.
Why Can One Person Have Multiple Curl Patterns?
It is extremely common for hair texture to vary across the scalp. Someone might have loose waves near the front, defined curls around the sides, and tighter curls toward the back of the head. Individual follicles do not have to be identical.
In fact, a 2026 systematic review of high-curl-pattern hair found that both hair density and curl pattern can vary within the same individual depending on scalp location, reinforcing why one person may have multiple textures across different areas of the head.
Differences in follicle shape, follicle orientation, hair diameter, growth characteristics, and the structure of individual fibers can create variations across different regions of the scalp. For that reason, broad curl classifications are useful descriptions, but they cannot capture every characteristic of an individual’s hair.
What Are the Different Curl Types?
One popular hair classification system groups textures into four broad categories:
- Type 1: Straight Hair
Hair has little to no natural curl or wave. - Type 2: Wavy Hair
Hair forms loose bends or S-shaped waves. - Type 3: Curly Hair
Hair forms more defined curls ranging from larger loops to tighter spirals. - Type 4: Coily Hair
Hair forms tight curls, coils, or zigzag patterns.
These categories are commonly divided further into A, B, and C classifications.
However, curl typing is primarily a descriptive system used in hair care. It is not a medical classification, and individual hair characteristics are considerably more complex than a single number and letter. Factors such as strand diameter, density, porosity, elasticity, and scalp condition can be just as important when determining how hair behaves and how it should be cared for.
Can Your Natural Curl Pattern Change?
Yes. Hair texture is largely influenced by genetics, but the hair that grows from a follicle does not necessarily remain identical throughout a person’s entire life. Several factors can affect texture.
Hormonal Changes
Hormonal changes may influence follicle activity and hair characteristics. Some people notice changes in texture during or after:
- Puberty
- Pregnancy
- Postpartum hormonal changes
- Perimenopause
- Menopause
- Other significant hormonal changes
Hair that was relatively straight earlier in life may become wavier or curlier, while naturally curly hair may sometimes become looser.
Aging
Hair commonly changes as people age. Individual strands may become finer, density may decrease, and changes within the follicle can affect texture. Sebum production may also decrease, making hair feel drier or behave differently than it did previously. For someone with curly or coily hair, these changes can affect curl definition even if the fundamental curl pattern has not completely changed.
Medical Conditions and Medications
Certain health conditions, nutritional deficiencies, hormonal disorders, and medications can affect hair growth and texture. A sudden, unexplained change in hair accompanied by significant shedding, thinning, scalp symptoms, or other physical changes may warrant evaluation by a healthcare professional or dermatologist.
Does Humidity Actually Make Hair Curlier?
For many people, yes. Hair readily interacts with moisture in the surrounding environment. Water can temporarily affect hydrogen bonds within keratin.
When humidity is high, hair absorbs moisture from the air. That can alter the arrangement of these temporary bonds and cause the strand to return more strongly toward its natural shape. For curly and wavy hair, this may mean increased curl or frizz. Straight hair may become wavier, while highly textured hair may expand in volume.
Unlike the stronger disulfide bonds within hair, hydrogen bonds can be broken and reformed relatively easily through water and heat. This is one reason hair may look completely different on a humid summer day than it does in dry winter air.
Can Heat Change Your Curl Pattern?
Heat styling can temporarily change the appearance of curly hair. A flat iron or blow dryer can alter weaker bonds within the hair, allowing curls to be temporarily straightened. Once exposed to moisture, those bonds can reform and the natural curl pattern typically returns. Repeated exposure to excessive heat is different. Significant heat damage can alter the structure and integrity of the hair shaft. Damaged curls may become:
- Looser
- Uneven
- Dry
- Brittle
- Difficult to define
- More susceptible to breakage
If the follicle itself remains healthy, new hair should generally grow according to its natural pattern even when older lengths have been damaged.
Does Hair Loss Affect Curl Pattern?
Hair loss doesn’t necessarily change the genetic curl pattern of individual follicles, but thinning can dramatically change how textured hair looks. Curl pattern, strand diameter, and density work together to create the appearance of volume.
Curly and coily hair can sometimes provide greater visual coverage because curved fibers occupy more space. When density decreases, however, curls may clump differently, scalp visibility may increase, and the overall hairstyle may lose volume.
Some forms of progressive hair loss can also cause follicular miniaturization, in which affected follicles produce progressively finer and shorter hairs. Changes in hair diameter can make the overall texture and appearance seem different even if the person’s fundamental curl characteristics remain.
Why Hair Texture Matters in Hair Restoration
Hair texture is an important consideration when designing a natural-looking hair restoration or hair replacement solution. Two people with the same number of hairs can appear to have very different levels of density depending on:
- Hair shaft diameter
- Curl pattern
- Hair color
- Contrast between the hair and scalp
- Hair length
- Styling
Curly hair can provide substantial visual coverage because each curved strand occupies more space than a completely straight strand. For hair transplantation, these characteristics can influence how grafts are distributed and the amount of visual coverage that can potentially be created with available donor hair.
Texture is equally important in non-surgical hair replacement. A customized hair system or wig should not simply match hair color. Curl pattern, wave, density, diameter, direction, and overall texture should work together to create a natural transition between replacement hair and the individual’s existing hair.
Matching Hair Texture in Hair Replacement Systems
Natural-looking hair replacement depends heavily on customization. When someone retains hair around the sides or back of the scalp, replacement hair should integrate with those existing characteristics.
An experienced hair replacement specialist may consider:
- Straight, wavy, curly, or coily texture
- Curl size and tightness
- Hair density
- Strand diameter
- Hair color and highlights
- Gray percentage
- Hair direction
- Desired length and style
The objective is not simply to provide more hair. It is to create hair that appears consistent with the individual. At Eldorado Hair Replacement Center, customized hair replacement solutions take these characteristics into account to help create a natural-looking result for men and women experiencing thinning or hair loss.
Frequently Asked Questions About Hair Curl Pattern
Is curly hair genetic?
Genetics plays a major role in determining whether hair grows straight, wavy, curly, or coily. Hair texture is a complex trait influenced by multiple genes rather than one single gene.
Does curly hair come from your mother or father?
Hair texture can be influenced by genes inherited from both parents. Because multiple genes are involved, a child’s hair does not necessarily have to closely match either parent’s texture.
What physically makes hair curly?
Curl develops through a combination of follicle shape and curvature, the way the hair fiber forms within the follicle, structural differences within the hair shaft, and the organization of proteins and chemical bonds within the hair.
Why did my straight hair suddenly become curly?
Hormonal changes, aging, certain medical circumstances, medications, and changes in follicular activity may affect hair texture. A dramatic unexplained change accompanied by hair loss or other symptoms should be discussed with a healthcare professional.
Can curly hair become straight naturally?
Hair texture can change over time, particularly during periods of hormonal change or aging. However, genetically curly hair does not typically become permanently straight simply because it is brushed, cut, or styled differently.
Does cutting curly hair make it curlier?
Cutting hair does not change the shape of the follicle. Removing length and weight can sometimes allow existing curls to spring upward more noticeably, creating the appearance of a tighter curl pattern.
Does shaving your head change your hair texture?
Shaving cuts the hair shaft at the surface and does not change the follicle underneath the skin. New growth may initially feel different because of the blunt cut end, but shaving itself does not permanently change the genetically influenced structure of the hair.
Why is my hair curlier underneath?
Different areas of the scalp can contain follicles with somewhat different characteristics. Environmental exposure, heat styling, chemical processing, and damage can also affect the outer layers of the hair more heavily than protected areas underneath.
Is curly hair more likely to break?
Curved hair fibers can be more susceptible to certain forms of mechanical stress and dryness, particularly when the curl pattern is tight. Appropriate conditioning, gentle handling, and limiting excessive heat or chemical damage can help reduce breakage.
Can hair grow back with a different texture after hair loss?
Sometimes regrowing hair can initially appear different in thickness, texture, or curl. Whether those changes persist depends on the cause of the hair loss and the health and characteristics of the follicle.
The Bottom Line
Hair curl pattern is much more complex than simply having “straight” or “curly” genes. The texture we see above the scalp reflects interactions among:
- Genetics
- Hair follicle shape and curvature
- Hair shaft structure
- Keratin organization
- Chemical bonds within the hair
- Hormonal influences
- Aging
- Moisture and environmental conditions
- Styling and hair damage
Most importantly, the follicle establishes many of the fundamental characteristics of the hair before the strand ever becomes visible above the scalp.
For people experiencing hair loss, these same characteristics become important when evaluating restoration and replacement options. Color alone isn’t enough to create natural-looking replacement hair. Texture, curl pattern, density, diameter, and growth direction all matter. Eldorado Hair Replacement Center provides customized hair restoration and hair replacement solutions designed around the individual characteristics of each client’s existing hair, appearance, and hair-loss needs. Contact us to book a free hair analysis and learn how we can help you regain your confidence and restore your hair.
