TCHH rs11803732: Hair Texture and Morphology
The single-nucleotide polymorphism rs11803732 is located within the trichohyalin (TCHH) gene on chromosome 1q21. Research has identified this locus as a key genetic factor influencing natural hair curliness, particularly in individuals of European ancestry. It represents a benign, non-medical trait variant that contributes to whether an individual has straight, wavy, or curly hair.
What each genotype means
Higher likelihood of curly hair
You carry two copies of the ancestral A allele at rs11803732 in the TCHH gene, which has been associated in European populations with a greater likelihood of wavy or curly hair. Hair shape is a complex multifactorial trait influenced by several other genes and environmental factors, so this genotype does not guarantee curly hair on its own. The association has primarily been evaluated in individuals of European ancestry and may not apply across other ancestral backgrounds.
Carried by approximately 35% to 40% of people of European descent and is the predominant genotype in East Asian populations.
Intermediate hair curliness likelihood
You carry one copy of the derived T allele and one ancestral A allele at rs11803732 in the TCHH gene. Each T allele statistically shifts the likelihood of hair texture toward straighter phenotypes in studies of European populations. Because hair morphology is polygenic, your natural hair shape is also guided by variations in genes such as EDAR, WNT10A, and FRAS1.
Carried by approximately 45% to 50% of individuals of European descent, but is very rare in East Asian populations.
Higher likelihood of straight hair
You carry two copies of the derived T allele at rs11803732 in the TCHH gene, a genotype associated with an increased probability of having straight hair in individuals of European ancestry. Research indicates that trichohyalin plays a structural role in the inner root sheath of the hair follicle, influencing fiber curliness. However, as hair texture is governed by multiple genetic variants across the genome, actual hair form varies among carriers.
Carried by approximately 12% to 16% of individuals of European descent and is extremely rare or absent in East Asian populations.
Genomic Context and the rs11803732 Variant
The single-nucleotide polymorphism rs11803732 is situated on chromosome 1 in the 1q21 genomic region, mapping to the trichohyalin (TCHH) gene locus. Genomic coordinates place this variant in close proximity and strong linkage disequilibrium with other widely studied hair-morphology markers, such as the missense variant rs11803731. Chromosome 1q21 contains the epidermal differentiation complex, a dense cluster of genes essential for skin barrier formation, hair growth, and cellular structural integrity. As cataloged in resources like dbSNP and the GWAS Catalog, rs11803732 involves a single base substitution that reflects normal human genetic diversity rather than a disease-causing mutation.
Biological Function of the TCHH Gene
The TCHH gene encodes trichohyalin, a crucial structural protein primarily expressed in the inner root sheath of developing hair follicles as well as the filiform papillae of the tongue. According to resources like MedlinePlus Genetics and GeneCards, trichohyalin acts as a mechanical stabilizer. During hair fiber development, it undergoes biochemical crosslinking with itself and with keratin intermediate filaments. This dense network forms a rigid cylinder around the growing hair strand, providing mechanical strength and shaping the cylindrical geometry of the fiber as it emerges from the skin surface.
Scientific Evidence and Hair Morphology Associations
Genome-wide association studies (GWAS), notably seminal research by Medland and colleagues published in the American Journal of Human Genetics, have implicated the TCHH locus in determining human hair curliness. In European cohorts, common variants across the TCHH region accounted for roughly 6% of the variance in hair texture, shifting the odds from curly or wavy toward straight hair. However, because hair texture is a polygenic trait influenced by numerous genomic loci—as well as mechanical forces and hormonal factors—the overall evidence strength for rs11803732 acting in isolation is categorized as limited to moderate. Having specific alleles modifies probabilities rather than guaranteeing a specific hair shape.
Ancestral Diversity and Allele Frequencies
Allele distributions for TCHH variants exhibit distinct geographic patterning. In populations of European descent, the minor allele frequency is approximately 0.38, reaching its highest prevalence among Northern European groups. In contrast, the variant is rare or absent in East Asian populations, where hair morphology is predominantly shaped by alleles in distinct genes, such as the EDAR and FGFR2 pathways. These divergence patterns underscore how human hair characteristics evolved through independent genetic mechanisms and neutral drift across different continental regions.
Interpreting Trait Results Responsibly
Discovering your rs11803732 genotype provides an educational glimpse into how hair biology functions at the molecular level, but it has no diagnostic or clinical utility. The variant does not indicate any medical condition, skin pathology, or hair-growth disorder. Because hair curliness is shaped by multiple interacting genes alongside personal grooming, humidity, age, and chemical treatments, an individual's actual hair phenotype may differ from the statistical tendencies suggested by this single genetic marker.
How common is this variant?
The minor allele occurs at an estimated frequency of approximately 0.38 in populations of European descent, where it is most common in Northern Europe. In contrast, the variant is rare or virtually absent in East Asian populations.
Frequently asked questions
Does rs11803732 determine whether my hair is straight or curly?
No single genetic variant determines hair texture on its own. While rs11803732 in the TCHH gene is associated with a statistical shift toward straighter or curlier hair, hair morphology is polygenic and shaped by multiple genes as well as environmental factors.
Is the rs11803732 variant related to hair loss or baldness?
There is no established association between rs11803732 and pattern baldness, alopecia, or hair shedding. The variant influences the structural geometry of the hair shaft rather than follicle lifespan or hormonal sensitivity.
Why is this variant common in Europeans but rare in East Asians?
Human populations developed different genetic variations influencing hair morphology after geographic divergence. In East Asian populations, hair texture and thickness are primarily driven by variations in genes like EDAR, whereas TCHH variants evolved predominantly in Western Eurasian lineages.
Can I use my rs11803732 genotype to choose hair care products?
Genetic results for rs11803732 reflect general population tendencies rather than the immediate physical state of your hair strand. Selecting hair care products is best done by observing your hair's actual porosity, thickness, and curl pattern directly.
Sources & further reading
Educational information only, last refreshed 9/11/2026. Not medical advice — these associations describe population statistics, not individual predictions.
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