Two siblings can grow up in the same house, eat the same food, use the same shampoo, and still end up with completely different hair. One stick-straight, the other a mass of curls that seems to have a mind of its own. It’s one of those traits that feels like it should come down to product or styling, but the truth is your hair texture was mostly decided long before you ever touched a brush.
It comes down to the shape of the follicle it grows out of, and that shape is written into your genes.
What Causes Curly Hair
Hair texture is largely determined by the shape of the hair follicle, the tiny pocket in your skin that each strand of hair grows from. A perfectly round, straight follicle produces straight hair. An oval or asymmetrical follicle causes the hair shaft to grow unevenly, curving as it comes out, which produces wavy, curly, or tightly coiled hair depending on just how asymmetrical that follicle is.
The Trichohyalin Gene and Others
Researchers have identified several genes involved in this process, with one of the most studied being TCHH, which codes for a protein called trichohyalin that helps give hair its structural shape. Variants in TCHH are strongly linked to straight versus curly hair in genome studies. Other genes, including ones involved in the shape of the follicle itself and the internal structure of the hair shaft, also play a role, which is why hair texture isn’t a simple one-gene, on-or-off trait. It’s more like a blend of multiple genetic dials, each nudging your hair a little more toward straight, wavy, curly, or coily.
This is also why curl pattern can vary so much within a single family. Hair texture inheritance doesn’t follow a simple dominant-or-recessive pattern the way eye color sometimes gets taught in school. It’s polygenic, meaning multiple genes contribute, so two curly-haired parents can have a straight-haired child, and vice versa.
How Common Is Curly Hair
Hair texture varies enormously by ancestry and population. Naturally curly or coily hair is especially common among people of African descent, while straighter hair textures are more common in East Asian populations, and wavy-to-curly textures show up widely across European and Mediterranean populations. Globally, straight hair is the most common texture overall, but curly and wavy hair combined still represent a very large share of the population, which is part of why hair-typing systems (like the well-known 1A through 4C scale) exist to describe the wide range in between.
Does Hair Texture Affect Your Health
Hair texture itself has no direct impact on your health. It’s a cosmetic and structural trait, not a functional one. That said, curlier and coilier hair types tend to be naturally drier, since the curves and bends in the hair shaft make it harder for natural oils from the scalp to travel down the length of the strand. This doesn’t cause any medical issue, but it’s part of why curly hair care routines often emphasize extra moisture and gentler handling than straight hair routines do.
What Your Hair Texture Genetics Mean for You
If you’ve ever wondered exactly which genetic variants are behind your specific curl pattern, or whether your texture leans more toward one parent’s genetics than the other, a detailed DNA report can break down the specific markers involved. It’s a fun way to put real science behind something you’ve been styling around your whole life.
Frequently Asked Questions
Can hair texture change over time even if it’s genetic?
Yes. Hormonal shifts, aging, pregnancy, and certain medications can all change how existing follicles produce hair, even though the underlying genetic blueprint doesn’t change. This is why some people notice their curl pattern shifting later in life.
Is curly hair dominant or recessive?
Neither, exactly. Hair texture is polygenic, meaning it’s influenced by multiple genes working together rather than a single dominant or recessive gene, which is why inheritance patterns can look inconsistent within families.
Why do identical twins sometimes have slightly different curl patterns?
Even with identical DNA, small differences in how genes are expressed, along with follicle-level developmental variation, can lead to subtle differences in curl pattern between identical twins.
Does cutting or shaving hair change its texture?
No. Cutting hair doesn’t affect the follicle shape that determines texture. Hair grows back with the same natural pattern regardless of how it’s cut.
Can two straight-haired parents have a curly-haired child?
Yes. Because multiple genes are involved, both parents can carry curl-related variants without showing much curl themselves, and still pass along a combination that produces curlier hair in their child.
Straight, wavy, curly, or coily, your hair texture is really just biology quietly doing its thing, one oddly shaped follicle at a time.